Bridging Phosphido Research Articles

Bridgehead isomer effects in bis(phosphido)-bridged diiron hexacarbonyl proton reduction electrocatalysts.

The influence of the substitution, orientation and structure of the phosphido bridges in [Fe2(CO)6(μ-PR2)2] electrocatalysts of proton reduction has been studied. The isomers e,a-[Fe2(CO)6{μ-P(Ar)H}2] (1a(Ar): Ar = Ph, 2'-methoxy-1,1'-binaphthyl (bn')), e,e-[Fe2(CO)6{μ-P(Ar)H}2] (1b(Ar): Ar = Ph, bn') were isolated from reactions of iron pentacarbonyl and the corresponding primary phosphine, syntheses that also afforded the phosphinidene-capped tri-iron clusters, [Fe3(CO)9(μ-CO)(μ3-Pbn')] (2) and [Fe3(CO)9(μ3-PAr)2] (3(Ar), Ar = Ph, bn'). A ferrocenyl (Fc)-substituted dimer [Fe2(CO)6{μ:μ'-1,2-(P(CH2Fc)CH2)2C6H4}] (4), in which the two phosphido bridges are linked by an o-xylyl group, was also prepared. The molecular structures of complexes 1a(Ph), 1b(Ph), 1b(bn'), 2 and 4 were established by X-ray crystallography. All complexes have been examined as electrocatalysts for proton reduction using p-toluene sulfonic acid in tetrahydrofuran. Cyclic voltammograms of the dimers with acid exhibit two catalysis waves for proton reduction. The first wave, which appears at the potential of the primary reduction, reaches maximum current (turnover) at moderate acid concentrations and is rapidly overtaken by the second wave, which appears at more negative potential. Both of these reductive waves show an initial first order dependence on acid. The electrochemistry and electrocatalyses of the [Fe2(CO)6(μ-PR2)2] dimers show subtle variations with the nature of the bridging phosphido group(s), including the orientation of bridgehead hydrogen atoms.

Synthesis and Characterization of Palladium Complexes Supported by an NPN-Phosphido Ancillary Ligand

The PdII coordination chemistry of the phosphido ligand [(2-Me2NC6H4)2P]− (NPN) is reported, along with the results of studies documenting the utility of such complexes as catalyst precursors for the Heck arylation of olefins. Examples of κ1-, κ2-, and κ3-NPN coordination to Pd are described. The secondary phosphine (NPN)H (1) was reacted with 0.5 equiv of [(C3H5)PdCl]2 to afford the dimeric species [(κ2-NPN)PdCl]2 (2) in 96% yield. Similarly, the reaction of 1 with 0.33 equiv of [Pd(OAc)2]3 led to the formation of dimeric [(κ2-NPN)PdOAc]2 (3) in 98% yield. Complexes 2 and 3 were both crystallographically characterized to reveal dipalladium species that feature bridging phosphido groups, as well as terminal chloride and acetate ligands, respectively. Treatment of 3 with Me3SiOTf resulted in the formation of the analogous triflate complex [(κ2-NPN)PdOTf]2 (4; 78% yield). Treatment of 2 with (C3H5)MgCl afforded the thermally sensitive, phosphido-bridged complex [(κ1-NPN)Pd(η3-C3H5)]2 (5) in 87% yield. The s...

Si−H Bond Activation by Electrophilic Phosphinidene Complexes

The terminal electrophilic phosphinidene complex [CpFe(CO)2{PN-i-Pr2}][AlCl4] (2), generated via chloride abstraction from [CpFe(CO)2{P(Cl)N-i-Pr2}] (1), reacts with primary, secondary, and tertiary silanes to form the silyl phosphine complexes [CpFe(CO)2{P(H)(SiR3)N-i-Pr2}][AlCl4] (3, SiR3 = SiPhH2; 4, SiR3 = SiPh2H; 5, SiR3 = SiEt3), in which the phosphinidene has inserted into the Si−H bond. A computational study shows that the insertion is concerted and has a triangular transition state. The silyl phosphine complexes 3, 4, and 5 are very susceptible to nucleophilic attack, which leads to P−Si bond cleavage and formation of the bridging phosphido complex [{CpFe(CO)}2(μ-CO){μ-P(H)N-i-Pr2}][AlCl4] (6).

Reactivity of mononuclear Pd(ii) and Pt(ii) complexes containing the primary phosphane (ferrocenylmethyl)phosphane towards metal chlorides and PPh3

The reaction of the primary phosphane (ferrocenylmethyl)phosphane [PH(2)CH(2)Fc, ] with an equimolar amount of [M(cod)Cl(2)] (cod = 1,5-cyclooctadiene, M = Pd, Pt) gave the unusual monobridged M(ii) dinuclear complexes of formula [(cod)ClM(micro-PHCH(2)Fc)M(PH(2)CH(2)Fc)Cl(2)] [M = Pt, ; M = Pd, ]. The mechanism leading to and involves the preliminary formation of cis-[M(PH(2)CH(2)Fc)(2)Cl(2)] which further reacts with free [M(cod)Cl(2)] before undergoing dehydrochlorination. The reaction of with PPh(3) led to the unexpected formation of the cyclic trinuclear complex [Pd(3)(micro-PHCH(2)Fc)(3)(PPh(3))(2)(PH(2)CH(2)Fc)Cl(3)] (). Further reaction of with PPh(3) led to the substitution of the tertiary phosphane for the primary one with formation of two geometric isomers and of formula [Pd(micro-PHCH(2)Fc)(PPh(3))Cl](3) differing only for the position of the PPh(3) group replacing the PH(2)CH(2)Fc ligand. In complex each micro-PHCH(2)Fc group bridging two palladium atoms has a terminal PPh(3) ligand in trans position with respect to the first Pd (the cis position being occupied by a chlorine) and a chlorine ligand trans to the other Pd (the cis position being occupied by a terminal PPh(3) ligand) thus rendering chemically equivalent the three PPh(3) (and the three phosphides). In complex the three terminal PPh(3) as well as the three bridging phosphido ligands are chemically inequivalent. Complexes and coexist in equilibrium in solution, but only precipitates from CH(2)Cl(2)-n-hexane yielding crystals suitable for X-ray analyses. These crystals are water/n-hexane solvates and belong to the monoclinic space P2(1)/c with a = 25.063(6) A, b = 15.564(4) A, c = 26.089(5) A, beta = 120.017(16) degrees . They contain two identical couples of enantiomers of . The peculiar arrangement of three metals and three phosphorus atoms of the bridging ligands ascertained for trimers , and has no precedent in the rich class of palladium and platinum phosphido chemistry.

Investigations on a Novel Silyl Transfer Reaction in Heterodimetallic Chemistry

Heterodinuclear silyl complexes of the type [(OC)3(R3Si)[Fe(mu-PPh2)Pt](CO)(PPh3)], which contain a [Fe(mu-P)Pt] triangular core, were previously reported to undergo an unprecedented dyotropic-type rearrangement involving migration of the silyl group from iron to platinum with concomitant 1,2 migration of CO from Pt to Fe. In the resulting complexes of formula [(OC)4[Fe(mu-PPh2)Pt](SiR3)(PPh3)], the Si atom occupies a cis position at the planar Pt center with respect to the phosphido bridge. DFT calculations were employed to elucidate the mechanism of this intramolecular silyl migration reaction. When the Fe-Pt precursor complex is [(OC)3(R3Si)[Fe(mu-PPh2)Pt](PPh3)2], the reaction sequence involves (i) the substitution of PPh3 by CO at Pt, (ii) the concerted migration of CO and SiR3, and (iii) the cis-trans isomerization at Pt. The calculations support the exergonic character of the overall process. An explanation for the experimental observation of only one product isomer being formed is possible via frontier molecular orbital analysis. Consistent with the experimental findings, the transition states of the migration (a species with a triply bridged intermetallic bond) and isomerization steps were found to be energetically within reach at room temperature. Additional support for the suggested mechanism also comes from the fact that relative silyl migration activities could be rationalized by the means of quantum chemistry.

Complexation and metallation of Ph 2PC [tbnd]C(CH 2) 5C [tbnd]CPh 2 in triosmium carbonyl clusters

Reaction of Ph 2PC C(CH 2) 5C CPh 2 with Os 3(CO) 10(NCMe) 2 affords Os 3(CO) 10(μ,η 2-(Ph 2P) 2C 9H 10) ( 1) and the double cluster [Os 3(CO) 10] 2(μ,η 2- (Ph 2P) 2C 9H 10) 2 ( 2), through coordination of the phosphine groups. Thermolysis of 1 in toluene generates Os 3(CO) 7(μ-PPh 2)(μ 3,η 5-Ph 2PC 9H 10) ( 3) and Os 3(CO) 8(μ-PPh 2)(μ 3,η 6-Ph 2P(C 9H 10)CO) ( 4). The molecular structures of 1, 3, and 4 have been determined by an X-ray diffraction study. Both 3 and 4 contain a bridging phosphido group and a carbocycle connected to an osmacyclopentadienyl ring, which are apparently derived from C–P bond activation and C–C bond rearrangement of the dpndy ligand governed by the triosmium clusters.

Generation and Reactions of Ruthenium Phosphido Complexes [(η5‐C5H5)Ru(PR′3)2(PR2)]: Remarkably High Phosphorus Basicities and Applications as Ligands for Palladium‐Catalyzed Suzuki Cross‐Coupling Reactions

Reactions of [(eta5-C5H5)Ru(PR'3)2(Cl)] with NaBAr(F) [BAr(F)-=B{3,5-[C6H3(CF3)2]}4-; PR'3=PEt3 or 1/2Et2PCH2CH2PEt2) (depe)] and PR2H (R=Ph, a; tBu, b; Cy, c) in C6H5F, or of related cationic Ru(N2) complexes with PR2H in C6H5F, gave the secondary phosphine complexes [(eta5-C5H5)Ru(PR'3)2(PR2H)]+ BAr(F)- (PR'3=PEt3, 3 a-c; 1/2depe, 4 a,b) in 65-91 % yields. Additions of tBuOK (3 a, 4 a; [D6]acetone) or NaN(SiMe3)2 (3 b,c, 4 b; [D8]THF) gave the title complexes [(eta5-C5H5)Ru(PEt3)2(PR2)] (5 a-c) and [(eta5-C5H5)Ru(depe)(PR2)] (6 a,b) in high spectroscopic yields. These complexes were rapidly oxidized in air; with 5 a, [(eta5-C5H5)Ru(PEt3)2{P(=O)Ph2}] was isolated (>99 %). The reaction of 5 a and elemental selenium yielded [(eta5-C5H5)Ru(PEt3)2{P(=Se)Ph2}] (70 %); selenides from 5 c and 6 a were characterized in situ. Competitive deprotonation reactions showed that 5 a is more basic than the rhenium analog [(eta5-C5H5)Re(NO)(PPh3)(PPh2)], and that 6 b is more basic than PtBu3 and P(iPrNCH2CH2)3N. The latter is one of the most basic trivalent phosphorus compounds [pK(a)(acetonitrile) 33.6]. Complexes 5 a-c and 6 b are effective ligands for Pd(OAc)2-catalyzed Suzuki coupling reactions: 6 b gave a catalyst nearly as active as the benchmark organophosphine PtBu3; 5 a, with a less bulky and electron-rich PR2 moiety, gave a less active catalyst. The reaction of 5 a and [(eta3-C3H5)Pd(NCPh)2]+ BF4- gave the bridging phosphido complex [(eta5-C5H5)Ru(PEt3)2(PPh2)Pd(NCPh)(eta3-C3H5)]+ BAr(F)- in approximately 90 % purity. The crystal structure of 4 a is described, as well as substitution reactions of 3 b and 4 b.

Formation and Characterization of the Hexanuclear Platinum Cluster [Pt6(μ-PBut2)4(CO)6](CF3SO3)2through Structural, Electrochemical, and Computational Analyses

The reaction between equimolar amounts of Pt(3)(mu-PBu(t)()(2))(3)(H)(CO)(2), Pt(3)()H, and CF(3)SO(3)H under CO atmosphere affords the triangular species [Pt(3)(mu-PBu(t)()(2))(3)(CO)(3)]X, [Pt(3)()(CO)(3)()(+)()]X (X = CF(3)SO(3)(-)), characterized by X-ray crystallography, or in an excess of acid, [Pt(6)(mu-PBu(t)()(2))(4)(CO)(6)]X(2), [Pt(6)()(2+)()]X(2)(). Structural determination shows the latter to be a rare hexanuclear cluster with a Pt(4) tetrahedral core formed by joining the unbridged sides of two orthogonal Pt(3) triangles. The dication Pt(6)()(2+)() features also extensive redox properties as it undergoes two reversible one-electron reductions to the congeners [Pt(6)(mu-PBu(t)()(2))(4)(CO)(6)](+) (Pt(6)()(+)(), E(1/2) = -0.27 V) and Pt(6)(mu-PBu(t)()(2))(4)(CO)(6) (Pt(6)(), E(1/2) = -0.54 V) and a further quasi-reversible two-electron reduction to the unstable dianion Pt(6)()(2)()(-)() (E(1/2) = -1.72 V). The stable radical (Pt(6)()(+)()) and diamagnetic (Pt(6)()) species are also formed via chemical methods by using 1 or 2 equiv of Cp(2)Co, respectively; further reduction of Pt(6)()(2+)() causes fast decomposition. The chloride derivatives [Pt(6)(mu-PBu(t)()(2))(4)(CO)(5)Cl]X, (Pt(6)()Cl(+)())X, and Pt(6)(mu-PBu(t)()(2))(4)(CO)(4)Cl(2), Pt(6)()Cl(2)(), observed as side-products in some electrochemical experiments, were prepared independently. The reaction leading to Pt(3)()(CO)(3)()(+)() has been analyzed with DFT methods, and identification of key intermediates allows outlining the reaction mechanism. Moreover, calculations for the whole series Pt(6)()(2+)() --> Pt(6)()(2)()(-)()( )()afford the otherwise unknown structures of the reduced derivatives. While the primary geometry is maintained by increasing electron population, the system undergoes progressive and concerted out-of-plane rotation of the four phosphido bridges (from D(2)(d)() to D(2) symmetry). The bonding at the central Pt(4) tetrahedron of the hexanuclear clusters (an example of 4c-2e(-) inorganic tetrahedral aromaticity in Pt(6)()(2+)()) is explained in simple MO terms.

Thermally induced dual P–C bond cleavage routes from the imido-capped cluster Ru 3(CO) 7(μ 3-CO)(μ 3-NPh)(bpcd): synthesis, spectroscopic properties, and X-ray diffraction structures of Ru 3(CO) 7(μ 3-CO)(μ 3-NPh)(bpcd), Ru 3(CO) 5(μ 2-CO) 2(μ 3-NPh)(μ 2-PPh 2)[μ,η 1,η 1-C [dbnd]C(PPh 2)C(O)CH 2C(O)], Ru 3(CO) 6(μ 2-CO)(μ 3-NPh)(μ-PhCO)[μ 2,η 2,η 1-PPhC [dbnd]C(PPh 2)C(O)CH 2C(O)], and Ru 3(CO) 9(μ 3-NPh)(μ 3-PPh)

The imido-capped cluster Ru 3(CO) 9(μ 3-CO)(μ 3-NPh) ( 1) reacts with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) to furnish both Ru 3(CO) 7(μ 3-CO)(μ 3-NPh)(bpcd) ( 2) and Ru 3(CO) 5(μ 3-CO)(μ 3-NPh)(bpcd) 2 ( 3) as the major and minor products, respectively, under thermal and Me 3NO activation. The thermolysis of cluster 2 affords the new triruthenium compounds Ru 3(CO) 5(μ 2-CO) 2(μ 3-NPh)(μ 2-PPh 2)[μ,η 1,η 1-C C(PPh 2)C(O)CH 2C(O)] ( 4), Ru 3(CO) 6(μ 2-CO)(μ 3-NPh)(μ-PhCO)[μ 2,η 2,η 1-PPhC C(PPh 2)C(O)CH 2C(O)] ( 5), and Ru 3(CO) 9(μ 3-NPh)(μ 3-PPh) ( 6). Compounds 2– 6 have been fully characterized in solution, and the molecular structures of 2, and 4– 6 have been determined. Cluster 2 exhibits a nido-NRu 3 core with a face-capping μ 3-CO and a chelating bpcd ligand that occupies an equatorial and axial site. VT 31P NMR data indicate that the bpcd ligand in 2 undergoes a rocking motion between the equatorial and axial sites at the attached ruthenium center at elevated temperatures. Cluster 4 possesses a similar nido polyhedral core that is tethered by a bridging phosphido group and the 3e-donor moiety μ 2,η 2,η 1-C C(PPh 2)C(O)CH 2C(O). The structure of 5 reveals a hypho architecture containing a single Ru–Ru bond and where the three ruthenium centers are bridged by imido and benzoyl moieties and the seven-electron donor ligand μ 2,η 2,η 1-PPhC C(PPh 2)C(O)CH 2C(O), which results from the cleavage of one the P–Ph bonds of the original bpcd ligand. The 50e cluster 6 exhibits a nido polyhedral core consisting of three Ru(CO) 3 groups that are capped by a μ 3-imido and μ 3-phosphinidine unit. Cluster 6 represents the first structurally characterized example of a mixed PhN/PhP capped cluster belonging to the family of nido-Ru 3(CO) 9(μ 3-EPh) 2 clusters. The pertinent structural highlights associated with these clusters are discussed, and the lack of reactivity of the capping imido group with the bpcd ligand in Ru 3(CO) 7(μ 3-CO)(μ 3-NPh)(bpcd) during thermolysis is contrasted with the related benzylidyne-capped cluster PhCCo 3(CO) 7(bpcd).

Synthesis and structures of (3-methyl-2-pyridyl)diphenylphosphane derivatives of metal clusters

An unsymmetric bidentate ligand (3-methyl-2-pyridyl)diphenylphosphane (P(Mepy)Ph 2) is able to react with various tetranuclear transition metal clusters such as HRuCo 3(CO) 12, HRuRh 3(CO) 12 and Rh 4(CO) 12. The synthesis and crystal structures of HRuCo 3(CO) 10(P(Mepy)Ph 2) ( 1), HRuRh 3(CO) 10(P(Mepy)Ph 2) ( 2), RuRh 2(CO) 9(P(Mepy)Ph) ( 3) and Rh 6(CO) 14(P(Mepy)Ph 2) ( 4) are described. In 1, 2 and 4 the phosphane ligand replaces the carbonyls and acts as a bridging bidentate P–N group. The formation of 3 includes degradation of both the metal cluster core and the ligand itself. One of the P–C bonds in the ligand is cleaved and the ligand caps a metal triangle with a bridging phosphido group together with the nitrogen donor. The reaction between dinuclear Rh 2(CO) 4Cl 2 and P(Mepy)Ph 2 gives a binuclear Rh 2(μ-CO)Cl 2(P(Mepy)Ph 2) 2 ( 5) with bridging ligands in a head-to-tail arrangement. The crystal structure is also given.

Dinuclear and Trinuclear Ni−, Pd−, and Pt−Halide Complexes of the Easily Accessible Chiral Ligand P,P,P-Tris[(+)-9-phenyldeltacyclan-8-yl]-1,2-bis(phosphanyl)benzene

The synthesis of seven dinuclear complexes [(+)δ-LMHal]2 (M = Ni, Pd, Pt; Hal = Cl, Br, I) is described, in which (+)δ-L− represents the deprotonated chiral chelate ligand P,P,P′tris[(+)-9-phenyldeltacyclan-8-yl]-1,2-bis(phosphanyl)benzene, easily accessible in a highly enantioselective homo-Diels−Alder reaction. All the dinuclear complexes are bent at the phosphido bridges which connect the two square-planar halves of the molecules. The phosphorus atoms of the phosphido bridges are stereogenic centers. For [(+)δ-LNiBr]2 and [(+)δ-LPdCl]2 both diastereomers with (SP,SP) and (RP,RP) configuration were observed, whereas for [(+)δ-LPdBr]2, [(+)δ-LPdI]2, and [(+)δ-LPtCl]2 only the (SP,SP) isomers could be obtained. Furthermore, the synthesis of eight trinuclear complexes [(+)δ-L2M3Hal4] (M = Pd, Pt; Hal = Cl, Br) is reported, which contain unusual three-square arrays. In the trinuclear complexes all the halogens are oriented to one side. Halogeno and phosphido bridges connect the three squares leading to chair configurations (opposite scaffold chirality possible) and boat configurations. For [(+)δ-L2Pd3Cl4], [(+)δ-L2Pd3Br4], and [(+)δ-L2Pt3Cl4] the two diastereomers with (SP,SP) and (RP,RP) configuration and for [(+)δ-L2Pt3Br4] the diastereomers with (SP,SP) and (SP,RP) configuration could be isolated. In addition, the dinuclear complex [(+)δ-LPt2Br3(cod)] (cod = 1,5-cyclooctadiene) containing a single phosphido bridge was obtained. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Regiospecific Reaction between Dimetallic Phosphido-Bridged W−W Complexes and Phosphane Imide − Electrophilic Site Switching by Metal−Metal Bond Formation

Reaction between CpW(CO)2(μ-PPh2)W(CO)5(W−W) (2) and Ph3P=NR (R = Pr, CH2Ph, iPr) in THF at refluxing temperature is regiospecific with the CNR ligand coordinated to the W(CO)4 unit to produce CpW(CO)2(μ-PPh2)W(CO)4(CNR)(W−W) (4). Spectroscopic data indicate that the complex exists in two stereoisomeric forms in solution. The structure of the cis isomer was determined by a single-crystal X-ray diffraction study which indicates that the CNR ligand is coordinated to the W atom of the W(CO)4 unit and cis to the phosphido bridge. Reaction between CpW(CO)3(μ-PPh2)W(CO)5 (1) and Ph3P=NR (R = Pr, CH2Ph, iPr) in THF under similar condition is also regiospecific. However, the CNR ligand is coordinated to the CpW site to produce CpW(CO)2(CNR)(μ-PPh2)W(CO)5 (3). There are also two stereoisomers of the complex, which were separated by column chromatography. Structures of both isomers were determined by single-crystal X-ray diffraction studies. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Phosphorus chemical shift tensors of phosphido ligands in ruthenium carbonyl compounds: (31)P NMR spectroscopy of single-crystal and powder samples and ab initio calculations.

The phosphorus chemical shift (CS) tensors of several ruthenium carbonyl compounds containing a phosphido ligand, micro), bridging a Ru [bond] Ru bond were characterized by solid-state (31)P NMR spectroscopy. As well, an analogous osmium compound was examined. The structures of most of the clusters investigated have approximate local C(2v) symmetry about the phosphorus atom. Compared to the "isolated" PH(2)(-) anion, the phosphorus nucleus of a bridging phosphido ligand exhibits considerable deshielding. The phosphorus CS tensors of most of the compounds have spans ranging from 230 to 350 ppm and skews of approximately zero. Single-crystal NMR was used to investigate the orientation of the phosphorus CS tensors for two of the compounds, Ru(2)(CO)(6)(mu(2)-C [triple bond] C [bond] Ph)(mu(2)-PPh(2)) and Ru(3)(CO)(9)(mu(2)-H)(mu(2)-PPh(2)). The intermediate component of the phosphorus CS tensor, delta(22), lies along the local C(2) axis in both compounds. The least shielded component, delta(11), lies perpendicular to the Ru [bond] P [bond] Ru plane while the most shielded component, delta(33), lies perpendicular to the C [bond]P [bond] C plane. The orientation of the phosphorus CS tensor for a third compound, Ru(2)(CO)(6)(mu(2)-PPh(2))(2), was investigated by the dipolar-chemical shift NMR technique and was found to be analogous, suggesting it to be the same in all compounds. Ab initio calculations of phosphorus magnetic shielding tensors have been carried out and reproduce the orientations found experimentally. The orientation of the CS tensor has been rationalized using simple frontier MO theory. Splittings due to (99,101)Ru [bond] (31)P spin-spin coupling have been observed for several of the complexes. A rare example of (189)Os [bond] (31)P spin-spin splittings is observed in the (31)P MAS NMR spectrum of the osmium cluster, where (1)J((189)Os, (31)P) is 367 Hz. For this complex, the (189)Os nuclear quadrupolar coupling constant is on the order of several hundred megahertz.

Phosphorus–hydrogen bond cleavage on a Ph 2PH-substituted μ 3-thioxo dicobalt–iron cluster as a route to bridging phosphido and thiophosphine ligands

The secondary phosphine-substituted (at cobalt) mixed-metal dicobalt–iron complex [Co 2Fe(μ 3-S)(CO) 8(PPh 2H)] ( 1) can be prepared in good yield from the reaction of [Co 2Fe(μ 3-S)(CO) 9] with one equivalent of Ph 2PH in toluene. Also isolated in the reaction, as minor products, are the disubstituted (both at cobalt) complex [Co 2Fe(μ 3-S)(CO) 7(PPh 2H) 2] ( 2) and the trisubstituted species [Co 2Fe(μ 3-S)(CO) 6(PPh 2H) 3] ( 3). Thermolysis of 1 or 2 results in PH bond cleavage and the formation of the bis-phosphido-bridged species [Co 2Fe(μ 3-S)(μ-PPh 2) 2(CO) 6] ( 4) and [Co 2Fe(μ 3-S)(μ-PPh 2) 2(CO) 5(PPh 2H)] ( 5). Complex 5 can also be prepared more directly by treatment of 4 with one equivalent of Ph 2PH. The X-ray structure of the PhPMe 2 analogue of 5, [Co 2Fe(μ 3-S)(μ-PPh 2) 2(CO) 5(PPhMe 2)] ( 5′), reveals the phosphine to be cobalt-bound and occupying an equatorial site. Carbonylation of 4 results in coupling of one phosphido group with the sulphur cap to give the thiophosphine-bridged complex [Co 2Fe(μ 3-SPPh 2)(μ-PPh 2)(CO) 7] ( 6), while treatment of 1 with n-BuLi followed by RSCH 2Cl (R=Me, Ph) results in the formation of the previously reported thiophosphinomethane-bridged species [Co 2Fe(μ 3-S)(μ-PPh 2CH 2SR)(CO) 8] (R=Me 7a, Ph 7b). In contrast, interaction of 1 with n-BuLi followed by successive treatment with carbon disulphide and methyl iodide yields the dithiomethoxycarbonylphosphine-bridged complex [Co 2Fe(μ 3-S){μ-PPh 2C(SMe)S}(CO) 8] ( 8). Single crystal X-ray diffraction studies have been performed on complexes 5′ and 8.

Mixed chloride–phosphine complexes of the dirhenium core. Part 11. Reactions of [Re 2Cl 8] 2− with secondary phosphines, PCy 2H and PPh 2H

The reaction between the dirhenium(III,III) anion, [Re 2Cl 8] 2−, and the secondary phosphine, PCy 2H, yields a mixture of products as a result of disproportionation, namely, a dirhenium(II,III) chloride–phosphine complex 1,3,6-Re 2Cl 5(PCy 2H) 3 ( 1) and a dirhenium(IV) face-sharing bioctahedral compound with bridging phosphido groups, [Bu n 4N][Re 2(μ-PCy 2) 3Cl 6] ( 2). The diphenylphosphine analogue of 2, [Bu n 4N][Re 2(μ-PPh 2) 3Cl 6] ( 3) has been similarly prepared from the reaction of [Re 2Cl 8] 2− with PPh 2H. An interesting dirhenium(III,III) complex, [Bu n 4N] 2[Re 2(μ-PPh 2) 2(PPh 2H) 2Cl 6] ( 4) having both neutral terminal phosphines and anionic phosphido bridges, has also been isolated as an intermediate in the latter system. Crystal structures of 1– 4 have been determined by X-ray crystallography. The compounds were also characterized by cyclic voltammetry, IR and 31P NMR spectroscopy.

Kinetics and substitution mechanism in the reaction of the seven-coordinate complexes bis-μ-diphenylphosphido- and bis-μ-dimethylphosphido-octacarbonyldimolybdenum (MoMo) with tri-n-butyl-phosphine

The dinuclear phosphido-bridged molybdenum complexes [(CO) 4 Mo(μ-PR 2) 2M o(CO) 4] (R=Ph or Me) react with P(n-Bu) 3 to give the corresponding mono and bis-phosphine derivatives. A kinetic study of the first substitution in decalin indicates a CO-dissociative mechanism involving the coordinatively unsaturated intermediate [(CO 4) Mo(μ-PR 2) 2M o(CO) 3]. The overall substitution rate depends on the rate of CO dissociation, k 1, and on the rate of bimolecular attack by CO, k −1, and by P(n-Bu) 3, k 2, on the reactive intermediate. The nature of the substituents at the phosphido bridge markedly affects the value of k 1, which is higher for the phenyl compared with the methyl group. This is mainly due to a lower activation enthalpy (Δ H 1*=125 (Ph) versus 141 (Me) kJ mol −1), which may reflect a weakening of the MoCO bond in the presence of a more electron-withdrawing ligand in trans position. The values of the competition rate ratio k −1/ k 2, always largely greater than unity, show that attack of the small CO is favoured with respect to the large P(n-Bu) 3; this suggests that the steric crowding observed on the molecular structure of the starting seven-coordinate complexes should play an important role also on the reactivity of their six-coordinate intermediates.

Migratory insertion and CO substitution reactions of the β,γ-unsaturated esters and amides [Fe 2(CO) 5(μ-PPh 2)(μ-η 1:η 2-{NuC(O)CH 2}CCH 2}] (Nu=OMe, OEt, OPr i, NHPh, NHBu t): synthesis and characterisation of acyl-bridged [Fe 2(CO) 4L 2(μ-PPh 2)(μ-CO{CCH 2}CH 2C(O)Nu)] (L 2=dppm, dppe) and alkenyl-bridged [Fe 2(CO) 4{P(Ome) 3} 2(μ-PPh 2)(μ-η 1:η 2-{NuC(O)CH 2}CCH 2)

Reaction of the β,γ-unsaturated esters and amides [Fe 2(CO) 5(μ-PPh 2)(μ-η 1(O):η 1(C):η 2(C)-{NuC(O)CH 2}CCH 2)] (Nu=OMe, 1a; R=OEt, 1b; R=OPr i , 1c, R=NHPh, 1d, R=NHBu t , 1e) with dppe and dppm results in displacement of the acyl carbonyl and migratory insertion to give the α,β,-unsaturated acyl derivatives [Fe 2(CO) 4(η 2-dppe)(μ-PPh 2)(μ-CO{CCH 2}CH 2C(O)Nu)] (Nu=OMe, 2a; R=OEt, 2b; R=OPr i , 2c, R=NHPh, 2d, R=NHBu t , 2e) and [Fe 2(CO) 4(μ-dppm)(μ-PPh 2)(μ-CO{CCH 2}CH 2C(O)Nu)] (R=OMe, 3a; R=OEt, 3b; R=OPr i , 3c, R=NHPh, 3d), respectively. Single-crystal X-ray analyses of 2a and 3a has revealed that the dppe ligand in the former chelates, with one arm binding trans and one cis to the phosphido bridge, while the dppm and phosphido group in the latter both bridge the iron-iron bond and are trans to one another. In contrast, reaction of 1a– c with trimethylphosphite results in displacement of the ester carbonyl oxygen to give [Fe 2(CO) 5{P(OMe) 3}(μ-PPh 2)(μ-η 1(C):η 2(C)-{NuC(O)CH 2}CCH 2}] (Nu=OMe, 4a; R=OEt, 4b; R=OPr i , 4c) followed by CO substitution to give [Fe 2(CO) 4{P(OMe) 3} 2(μ-PPh 2)(μ-η 1(C):η 2(C)-{Nu(O)CCH 2}CCH 2)] (Nu=OMe, 6a; R=OEt, 6b; R=OPr i , 6c) with no evidence for the formation of the corresponding acyl-bridged derivative. Thermolysis of toluene solutions of 4a– c result in loss of CO and coordination of the oxygen atom of the ester carbonyl to give [Fe 2(CO) 4{P(OMe) 3}(μ-PPh 2)(μ-η 1(O):η 1(C):η 2(C)-{NuC(O)CH 2}CCH 2)] (Nu=OMe, 5a; R=OEt, 5b; R=OPr i , 5c), an intermediate in the formation of 6a– c. Complexes 5a and 6a have been characterised by single-crystal X-ray crystallography.

Novel metal-to-metal silyl-migration reactions in heterometallic complexes.

An unprecedented, intramolecular metal-to-metal silyl ligand migration reaction has been discovered in a series of phosphido-bridged iron-platinum complexes and which may be triggered by an external nucleophile. Thus, reaction of solutions of [(OC)3-(R1/3Si)Fe(mu-PR2R3)Pt(1,5-COD) (1a R1 = OMe, R2 = 3 = Ph; 1b R1 = OMe, R2 = R3 = Cy; 1c R1 = Ph, R2 = R3 = Ph; 1d R1 = Ph, R2 = R3 = Cy; 1e R1 = Ph, R1 = H, R3 = Ph) in CH2Cl2 with CO rapidly afforded the corresponding complexes [(OC)4Fe(mu-PR2R3)Pt(SiR1/3)-(CO)] (2a-e) in which the silyl ligand has migrated from Fe to Pt, while two CO ligands have been ligated, one on each metal. When 1a or 1c was slowly treated with two equivalents of tBuNC at low temperature, quantitative displacement of the COD ligand was accompagnied by silyl migration from Fe to Pt and coordination of an isonitrile ligand to Fe and to Pt to give [(OC)3-(tBuNC)Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)] (3a) and [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[SiPh3](CNtBu)] (3c). Reaction of 2a with one equivalent of tBuNC selectively led to substitution of the Pt-bound CO to give [(OC)4-Fe(mu-PCy2)Pt[Si(OMe)3](CNtBu)] (4b), which reacted with a second equivalent of tBuNC to give [(OC)4Fe(mu-PCy2)-Pt[Si(OMe)3](CNtBu)2] (5b) in which the metal-metal bond has been cleaved. Opening of the Fe-Pt bond was also observed upon reaction of 3a with tBuNC to give [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)2] (6). The silyl ligand migrates from Fe, in which it is trans to mu-PR2R3 in all the metal-metal-bonded complexes, to a position cis to the phosphido bridge on Pt. However, in 5a,b and 6 with no metal-metal bond, the Pt-bound silyl ligand is trans to the phosphido bridge. The intramolecular nature of the silyl migration, which may be formally viewed as a redox reaction, was established by a cross-over experiment consisting of the reaction of 1a and 1d with CO; this yielded exclusively 2a and 2d. The course of the silyl-migration reaction was found to depend a) on the steric properties of the -SiR1/3 ligand, and for a given mu-PR2R3 bridge (R2 = R3 = Ph), the migration rate decreases in the sequence Si(OMe)3> SiMe2Ph> SiMePh2>>SiPh3; b) on the phosphido bridge and for a given silyl ligand (R1 = OMe), the migration rate decreases in the order mu-PPh2 >> mu-PHCy; c) on the external nucleophile since reaction of 1c with two equivalents of P(OMe)3, P(OPh)3 or Ph2PCH2C(O)Ph led solely to displacement of the COD ligand with formation of 11a-c, respectively, whereas reaction with two equivalents of tBuNC gave the product of silyl migration 3c. Reaction of [(OC)3-[(MeO)3Si]Fe(mu-PPh2)Pt(PPh3)2] (7a) with tBuNC (even in slight excess) occurred stereoselectively with replacement of the PPh3 ligand trans to mu-PPh2, whereas reaction with CO led first to [(OC)3((MeO)3Si)Fe(mu-PPh2)Pt(CO)-(PPh3)] (8a), which then isomerized to the migration product [(OC)4Fe(mu-PPh2)Pt[Si(OMe)3](PPh3)] (9a). Most complexes were characterized by elemental analysis, IR and 1H, 31P, 13C, and 29Si NMR spectroscopy, and in five cases by X-ray diffraction.

Modern aspects on tri- and tetranuclear cluster complexes supported by phosphido bridges

This report on small cluster complexes with metal-metal bonds in the field of coordination chemistry documents results in the following scientific areas. (1) Systematic synthetic routes via ditransition metal carbonyl derivative of manganese and rhenium (group 7) to functionalizedtriangulo- andtetrahedro-clusters including structural characterization, (2) Dynamic properties of mono- and diauration isomers like M2(μ-AuPR3)(μ-PCyH)(CO)8/M2(μ-H)(μ3-PCy(AuPR3))(CO)8 (isomerization) and M2(μ-AuPR3)2(μ4-PCy)(CO)8/M2(μ-AuPR3)(μ3-PCy(AuPR3))(CO)8 (M = Mn, Re; R = organic residue) (rearrangement and valence isomerization) and MM’(μ-H)(μ-PCy2)(μ4-PCy(AuPR3))(CO)6 (M = M’, M ≠ M’) (topomerization) going from one to the other homologue and the kinetic study of isomerization in the framework Re2(AuPCy3)2(μ-PMeN2(μ-C(Bu)O)(CO)6, (3) Correlations of chirality transfer in diastereomerictetrahedro-clusters Re2(M1PR3)2(μ-PCy2)(CO)7(η1-L*) (M1 = coin metals, L* = chiral ligand as (+) or (-) prolinate, for example) from CD data. These selected contributions will be discussed to answer the question “Do small cluster complexes remain as a future challenge in cluster chemistry?”

Synthesis and characterization of a series of novel nickel(II)/nickel(I) complexes. Crystal structures of [NiCl2(dcpm)], [Ni(dcpm)2](NO3)2·2EtOH, [Ni2Cl2(μ-dcpm)2(μ-H)] and [Ni2(μ-PCy2)2(PCy2Me)2]; dcpm=bis(dicyclohexylphosphino)methane

The complexes [(dcpm)NiCl2] (1), [Ni2Cl2(μ-dcpm)2(μ-H)] (3), [Ni2(μ-PCy2)2(PCy2Me)2] (4) and [Ni(dcpm)2](NO3)2·2EtOH (2), dcpm=bis(dicyclohexylphosphino)methane, have been prepared and characterized by 31P, 1H NMR (or EPR) as well as X-ray crystallography. The salt NiCl2·6H2O was found to react with dcpm to form the monomeric, four-coordinate, diamagnetic complex [(dcpm)NiCl2] (1). Compound 1 was then reduced with nBu3SnH (or LiH with heating) in toluene at room temperature to form the air sensitive ‘A-frame’ complex [Ni2Cl2(μ-dcpm)2(μ-H)] (3). The Ni-Ni bond distance for 3 was found to be 2.904(3) Å showing a lack of any Ni-Ni metal bonding. [Ni2(μ-PCy2)2(PCy2Me)2] (4) was then formed by the reaction of 1 and excess LiH, heating to 90°C in an oil bath. [Ni2Cl2(μ-dcpm)2(μ-H)] (3) was shown to be an intermediate in the synthesis of the bridging phosphido nickel complex. The Ni-Ni bond distance in 4 is 2.3910(8) Å corresponding to a single Ni-Ni metal bond. The reaction of Ni(NO3)2·6H2O with dcpm in ethanol yields the square planar complex [Ni(dcpm)2](NO3)2·2EtOH (2).