Phosphinidene-bridged Complexes Research Articles

Heterometallic phosphinidene-bridged complexes derived from the phosphanyl complexes syn-[MCp(PHR*)(CO)2] (M = Mo, W; R* = 2,4,6-C6H2tBu3)

The title phosphanyl complexes were prepared upon photolysis of equimolar mixtures of dimers [M2Cp2(CO)6] and PH2R* (R* = 2,4,6-C6H2tBu3). They were converted into the corresponding chlorophosphanyl derivatives syn-[MCp(PClR*)(CO)2] upon reaction with CCl4, while its deprotonation (M = Mo) yielded the phosphinidene Li[MoCp(PR*)(CO)2]. These mononuclear precursors were tested for the synthesis of heterometallic PR*-bridged derivatives by following three synthetic strategies. Photochemical reactions between phosphanyl complexes and dimers [M´2(CO)2n] or [M´2Cp2(CO)2n] (M’ = Mn, Re, Fe, Ru, Co) gave binuclear derivatives of types [MM´Cpx(μ-PR*)(CO)n+2] and [MoM´Cpx(μ-PR*)(CO)n+1] (x = 1,2), but yields were very poor except for the WRe complexes. Combinations with Co, Mn, and Re were best made through reaction between carbonylates [M’(CO)n]− and chlorophosphanyl complexes, to give respectively the pentacarbonyl [MoCoCp(μ-PR*)(CO)5] and the heptacarbonyls [MM´Cp(μ-PR*)(CO)7] (MM’ = MoRe, MoMn, WMn). The latter were easily decarbonylated thermally to give hexacarbonyls [MM´Cp(μ-PR*)(CO)6], which display heterometallic single bonds and short M−P distances of ca. 2.27 Å formulated as double M=P bonds, and rearranged upon thermal or photochemical activation to give the hydride-phosphanyl derivatives [MM´Cp(μ-H){μ-P(CH2CMe2)C6H2tBu2}(CO)6]. This process was suppressed in the photochemical reactions by using a THF/NCMe (10:1) mixture as solvent, but then the acetonitrile complexes [MoM´Cp(μ-PR*)(CO)5(1κ-NCMe)] were formed. Combinations with Fe and Ru were best prepared by reacting Li[MoCp(PR*)(CO)2] with halide complexes [MXCp(CO)2], to give the tetracarbonyls [MoM´Cp2(μ-PR*)(CO)4] (M’ = Fe, Ru), a method also useful to prepare the gold complex [MoAuCp(μ-PR*)(CO)2{P(p-tol)3}] upon reaction with [AuCl{P(p-tol)3}]. The above tetracarbonyl complexes were decarbonylated photochemically to give the metal-metal bound tricarbonyls [MoM´Cp2(μ-PR*)(CO)3].

P[sbnd]C coupling reactions of pyramidal phosphinidene-bridged dimolybdenum complexes with alkynes

The new pyramidal phosphinidene-bridged complex [Mo2Cp(μ-κ1: κ1,η5-PC5H4)(η6-HMes*)(CO)2{P(OMe)3}] (2b) was prepared in situ upon reaction of the trigonal phosphinidene complex [Mo2Cp(μ – κ1: κ1, η5-PC5H4)(η6-HMes*)(CO)2] (1) with P(OMe)3. This complex underwent an unexpected Michaelis-Arbuzov-like rearrangement when dissolved in tetrahydrofuran, to give the phosphanyl-phosphonate isomer [Mo2Cp{μ – κ1: κ1, η5-P(Me)C5H4}(η6-HMes*)(CO)2{P(O)(OMe)2}] in a quantitative way. The reactions of complex 2b, and also its PMe3 analogue [Mo2Cp(μ – κ1: κ1, η5-PC5H4)(η6-HMes*)(CO)2(PMe3)] (2a), with different internal alkynes (EtCCC(O)Me and MeCCCO2Me) and terminal alkynes (HCCR; R = 4-C6H4Me, C(O)Me, CO2Me) were then investigated. These reactions proceeded in all cases rapidly at room temperature (less than 1 min) with very high regioselectivity, to give the corresponding metallacyclic products [Mo2Cp{ μ – κ2P,C: κ1P, η5-P(C5H4)CR1CR2C(O)}(η6-HMes*)(CO)(PX3)] in high yield (X = Me, OMe; R1 = Et, Me, H; R2 = C(O)Me, CO2Me, 4-C6H4Me). Spectroscopic data for these complexes indicate that they all share the same structure, further confirmed through an X-ray single crystal study on the EtCCC(O)Me derivative of compound 2b.

ChemInform Abstract: Iron‐ and Cobalt‐Catalyzed Synthesis of Carbene Phosphinidenes.

In the presence of stoichiometric or catalytic amounts of [M{N(SiMe3)2}2] (M=Fe, Co), N-heterocyclic carbenes (NHCs) react with primary phosphines to give a series of carbene phosphinidenes of the type (NHC)·PAr. The formation of (IMe4)·PMes (Mes=mesityl) is also catalysed by the phosphinidene-bridged complex [(IMe4)2Fe-(m-PMes)]2, which provides evidence for metal-catalysed phosphinidene transfer.

Gold(I) and related heterometallic derivatives of dimolybdenum complexes with asymmetric phosphinidene bridges.

The phosphinidene-bridged complexes [Mo2Cp2(μ-κ(1):κ(1),η(6)-PR*)(CO)2] (1), [Mo2Cp2(μ-κ(1):κ(1),η(4)-PR*)(CO)3] (2), [Mo2Cp(μ-κ(1):κ(1),η(5)-PC5H4)(η(6)-HR*)(CO)2] (3), and [Mo2Cp2(μ-κ(1):κ(1)-PH)(η(6)-HR*)(CO)2] (4) were examined as precursors of heterometallic gold(I) and related derivatives (Cp = η(5)-C5H5, R* = 2,4,6-C6H2(t)Bu3). These complexes reacted with [AuCl(THT)] to give the corresponding derivatives [AuMo2ClCp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2], [AuMo2ClCp2(μ-κ(1):κ(1):κ(1),η(4)-PR*)(CO)3] (Au-Mo = 2.8493(6) Å), [AuMo2ClCp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)], and [AuMo2ClCp2(μ3-PH)(CO)2(η(6)-HR*)] formally resulting from the addition of an acceptor AuCl moiety to the short Mo-P bond of the parent substrates almost perpendicular to the corresponding Mo2P plane. The chloride ligand was easily displaced upon reaction of the PC5H4-bridged gold complex with K[MoCp(CO)3] to give the tetranuclear derivative [AuMo3Cp2(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)5(η(6)-HR*)] (Au-Mo = 2.711(2) and 2.807(2) Å). Compound 1 also reacted with HgI2 to give a hexanuclear complex [HgMo2Cp2(μ-I)I(μ-κ(1):κ(1),η(6)-PR*)(CO)2]2 containing dative Mo→Hg bonds (2.820(1) and 2.827(1) Å), whereas complex 3 gave the μ3-PR bridged complex [HgMo2CpI2(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)]. Complexes 1 to 4 also reacted easily with [AuL(THT)]PF6 (L = THT, P(p-tol)3, PMe3, P(i)Pr3) to give the corresponding cationic trinuclear derivatives [AuMo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2L](PF6) (Au-Mo = 2.8080(3) Å for L = P(p-tol)3), [AuMo2Cp2(μ-κ(1):κ(1):κ(1),η(4)-PR*)(CO)3L](PF6), and [AuMo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*){P(p-tol)3}](PF6). The blue, analogous PH-bridged complexes were more conveniently isolated as tetra-arylborate salts [AuMo2Cp2(μ3-PH)(CO)2(η(6)-HR*)L](BAr'4) (Au-Mo = 2.8038(6) Å for L = P(i)Pr3; Ar'= 3,5-C6H3(CF3)2]. Compounds 1, 3, and 4 reacted readily with the cation [Au(THT)2](+) (as PF6(-) or BAr'4(-) salts) in a 2:1 ratio to give respectively the corresponding pentanuclear derivatives [Au{Mo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2}2](PF6), [Au{Mo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)}2](PF6) (Au-Mo = 2.7975(7) and 2.8006(7) Å), and [Au{Mo2Cp2(μ3-PH)(CO)2(η(6)-HR*)}2](BAr'4) (Au-Mo = 2.8233(8) and 2.8691(7) Å). Related silver complexes were obtained from the reaction of 3 and 4 with [AgCl(PPh3)]4 after spontaneous symmetrization, while reaction of 1 with [Cu(NCMe)4]PF6 in a 2:1 ratio yielded the analogous copper complex [Cu{Mo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2}2](PF6). All the above cationic gold complexes having (μ-κ(1):κ(1):κ(1),η(6)-PR*) ligands (but not the copper complex) rearranged into [Au{Mo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)}2](PF6) in refluxing 1,2-dichloroethane solution.

Reactions of the phosphinidene-bridged complexes [Fe2(η5-C5H5)2(μ-PR)(μ-CO)(CO)2] (R = Cy, Ph) with electrophiles based on p-block elements

The title complexes reacted readily with the methylating agents MeI and CF(3)SO(3)Me, chalcogens (O(2), S(8)) and borane adducts BH(3)·L (L = THF, N(t)Bu(3), PPh(3)) to initially give the corresponding neutral or cationic derivatives of the type [Fe(2)Cp(2){μ-P(E)R}(μ-CO)(CO)(2)](n) (Cp = η(5)-C(5)H(5); n = 0, E = O, S, BH(3); n = +1, E = Me), which could be further functionalized through additional reactions. Thus, the oxophosphinidene complex [Fe(2)Cp(2){μ-P(O)Cy}(μ-CO)(CO)(2)] could be protonated or alkylated with HBF(4)·OEt(2) or CF(3)SO(3)Me, to give the complexes [Fe(2)Cp(2){μ-P(OR')Cy}(μ-CO)(CO)(2)](+) (R' = H, Me) respectively, while the photochemical treatment of compounds [Fe(2)Cp(2){μ-P(BH(3))R}(μ-CO)(CO)(2)] gave the dicarbonyl derivatives [Fe(2)Cp(2){μ-κ(1):κ(1),η(2)-P(BH(3))R}(μ-CO)(CO)], with a phosphinidene-borane ligand displaying coordination of a B-H bond to one of the iron atoms in a side-on fashion (Fe-H = 1.78(4) Å, Fe-B = 2.351(5) Å for the PCy compound). The title complexes also reacted readily with 3,5-di-tert-butyl-o-benzoquinone or benzyl azide. The first reaction gave the phosphonite complex [Fe(2)Cp(2)(μ-CO)(2)(CO){P(O(2)C(6)H(2)(t)Bu(2))R}], while the second reaction yielded initially the corresponding 1 : 1 adducts [Fe(2)Cp(2){μ-P(N(3)CH(2)Ph)R}(μ-CO)(CO)(2)], with a P:P-bound phosphatriazadiene ligand. The PCy compound underwent clean denitrogenation in toluene at 368 K to give the iminophosphinidene complex [Fe(2)Cp(2){μ-P(NCH(2)Ph)Cy}(μ-CO)(CO)(2)], which in turn could be protonated selectively with [NH(4)]PF(6) at the P-bound nitrogen atom, to yield the aminophosphide derivative [Fe(2)Cp(2){μ-P(NHCH(2)Ph)Cy}(μ-CO)(CO)(2)]PF(6) (Fe-Fe = 2.6362(8) Å). Denitrogenation could be also induced photochemically on the phosphatriazadiene complex, but this also caused fragmentation and recombination of different bonds to give the trinuclear compound [Fe(3)Cp(3)(μ(3)-PCy){μ-κ(1):κ(1)-C(O)(NHCH(2)Ph)}(μ-CO)(2)], having phosphinidene and C:O-bound aminoacyl ligands bridging the metal atoms.

Symmetrization in a Phosphinidene-Bridged Complex To Give a Diphosphanediyl Derivative with Metal-Centered Reactivity

The phosphinidene complex [Mo(2)Cp(μ-κ(1):κ(1),η(5)-PC(5)H(4))(CO)(2)(η(6)-HMes*)] reacts with CO to give the diphosphanediyl derivative [Mo(2){μ-κ(1),η(5):κ(1),η(5)-(C(5)H(4))PP(C(5)H(4))}(η(6)-HMes*)(2)]. The latter compound features unreactive lone electron pairs at phosphorus, which instead contribute to the electronic communication between metal centers via a weak π(PP)-bonding interaction. As a result, this complex displays metal-centered acid-base and redox behavior.

Structure, Bonding, and Reactivity of Binuclear Complexes Having Asymmetric Trigonal Phosphinidene Bridges: Addition of 16-Electron Metal Carbonyl Fragments to the Dimolybdenum Compounds [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(CO)2L] and [Mo2Cp2(μ-PH)(CO)2L] (L = η6-1,3,5-C6H3tBu3)

The phosphinidene-bridged complexes [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(CO)2L] and [Mo2Cp2(μ-PH)(CO)2L] (Cp = η5-C5H5; L = η6-1,3,5-C6H3tBu3) react readily with [Fe2(CO)9] or the solvate complexes [M(CO)5(THF...

Nucleophilic and Electrophilic Behavior of the Phosphinidene-Bridged Complex [Fe2(η5-C5H5)2(μ-PCy)(μ-CO)(CO)2

The phosphinidene-bridged complex [Fe2Cp2(μ-PCy)(μ-CO)(CO)2] (1) reacts with HC≡CR (R = p-tol, CO2Me) to give products incorporating one or two alkyne molecules and involving further coupling with Cp or CO ligands, as shown by the formation of the complexes [Fe2Cp{μ-η5:κ1-C5H4PCyCHCH(p-tol)}(CO)3], [Fe2Cp2{μ-κ1:κ1,η1-CyPCHC(p-tol)C(O)}(μ-CO)(CO)], and [Fe2Cp2(μ-CO)2(CO){PCy(CHCHCO2Me)(C2CO2Me)}]. In contrast, the reactions of 1 with benzyl azide or (trimethylsilyl)diazomethane initially give the simple 1:1 adducts [Fe2Cp2(μ-CyPN3CH2Ph)(μ-CO)(CO)2] and [Fe2Cp2{μ-CyPN2CH(SiMe3)}(μ-CO)(CO)2], respectively, although the latter rearranges to yield [Fe2Cp2{μ-κ1:κ1,η1-CyPN(SiMe3)NCH}(μ-CO)(CO)] under photolytic conditions.

Formation and Cleavage of P−C, Mo−C, and C−H Bonds Involving Arylphosphinidene and Cyclopentadienyl Ligands at Dimolybdenum Centers

The phosphinidene-bridged complex [Mo2Cp2(μ-PR*)(CO)4] (R = 2,4,6- C6H2tBu3) experiences an intramolecular C−H bond cleavage from a tBu group to give the phosphide-hydride derivative [Mo2Cp2(μ-H){μ-P(CH2CMe2)C6H2tBu2}(CO)4] in refluxing diglyme (ca. 438 K) or under exposure to near-UV−visible light. In contrast, its exposure to UV light yields two different dicarbonyl derivatives depending on the reaction conditions, either the triply bonded [Mo2Cp2(μ-PR*)(μ-CO)2] (Mo−Mo = 2.5322(3) Å) or its isomer [Mo2Cp2(μ-κ1:κ1,η6-PR*)(CO)2], in which the phosphinidene ligand bridges asymmetrically the metal centers while binding its aryl group to one of the molybdenum atoms in a η6-fashion. The latter complex experiences a proton-catalyzed tautomerization to yield the cyclopentadienylidene−phosphinidene derivative [Mo2Cp(μ-κ1:κ1,η5-PC5H4)(η6-R*H)(CO)2]. Carbonylation of the η6-phosphinidene complex proceeds stepwise through the η4-tricarbonyl complex [Mo2Cp2(μ-κ1:κ1,η4-PR*)(CO)3] and then to the starting tetracarbonyl compound, whereas its reaction with CNtBu yields only the η4-complex [Mo2Cp2(μ-κ1:κ1,η4-PR*)(CNtBu)(CO)2], which was characterized through an X-ray study. The η4-tricarbonyl species reacts with CNtBu in tetrahydrofuran to give the metal−metal bonded derivative [Mo2Cp2(μ-PR*)(CNtBu)(CO)3]. In petroleum ether, however, this reaction yields the bis(isocyanide) derivative [Mo2Cp2(μ-PR*)(CNtBu)2(CO)3], which has an asymmetric trigonal phosphinidene bridge and no metal−metal bond. All the above results can be explained by assuming the operation of two primary processes in the photolysis of [Mo2Cp2(μ-PR*)(CO)4], one of them involving a valence tautomerization of the phosphinidene ligand, from the trigonal (four-electron donor) to the pyramidal (two-electron donor) coordination mode. The carbonylation reaction of the η6-complex is accelerated by the presence of CuCl, due to the formation of the trimetal species [CuMo2(Cl)Cp2(μ-κ1:κ1:κ1,η6-PR*)(CO)2] and [CuMo2(Cl)Cp2(μ-κ1:κ1:κ1,η4-PR*)(CO)3]. The latter complexes were also characterized by single-crystal X-ray studies.

Syntheses, Crystal Structures and Reactivity of Organometallic Tantalum(IV) Phosphinidene Complexes: trans-[{Cp*TaCl(μ-PR)}2] (Cp* = C5Me5, R = Cy, tBu, Ph), cis- and trans-[{Cp*TaCl(μ-PMes)}2] (Mes = 2,4,6-Me3C6H2) and cis-[{Cp′TaCl(μ-PMes)}2] (Cp′ = C5H4Me)

The reaction of [Cp*TaCl4] (Cp* = C5Me5) with LiPHR (1:1 or 1:2) gives the phosphinidene-bridged tantalum(IV) complexes trans-[{Cp*TaCl(μ-PR)}2] [R = Cy (1), tBu (2), Ph (3), 2,4,6-Me3C6H2 (Mes) (4b)]. When the reaction with LiPHMes is carried out in a 1:1 ratio, cis-[{Cp*TaCl(μ-PMes)}2] (4a) is also formed besides 4b. For comparison, cis-[{Cp′TaCl(μ-PMes)}2] (5) was prepared from [Cp′TaCl4] (Cp′ = C5MeH4) and LiPHMes (1:1). 1−5 are diamagnetic and were characterised spectroscopically (IR, MS; 1 H, 31P, 13C NMR). Crystal structure determinations on 1−5 showed the presence of dimeric phosphinidene-bridged TaIV complexes. The phosphinidene-bridged complexes 1, 3 and 4b do not react with acetone, benzophenone, acetonitrile, CS2 (1, 3), acetaldehyde (4b), or ethylaluminum dichloride (3). 3 reacts with moist acetone in the presence of traces of air to give the trinuclear cluster [{Cp*TaCl(μ2−O)}3(μ3-O)(μ2-O2PHPh)}] (6) in very low yield. With an excess of CyNC, 3 gives [Cp*TaCl(CNCy)4]Cl (7), which was characterised by 1H and 13C NMR spectroscopy and by crystal structure determination. As a minor product, [(Cp*TaCl2)2(μ2-O)(η2,μ2-P2Cy2)] (8) was also obtained in the reaction of [Cp*TaCl4] with LiPHCy. 6 and 8 were only characterised by crystal structure determination. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Formation of metal-element double bonds by chlorosilane elimination

Transition metal complexes, capable of chlorosilane elimination to give metal—element double bonds, are generated as transient species by two novel methods. The first one involves reaction of anionic silyl complexes with geminal dihalides and is exemplified by reactions of [MeCp(CO)2Mn-SiR3]− with dihalides of carbon and main-group V elements. Formation of carbene complexes and phosphinidene-bridged complexes, [MeCp(CO)2Mn]2PR, proves that the anionic silyl complex can be used as an equivalent for [MeCp(CO)2Mn]2− in the synthesis. The second method proceeds by oxidative addition of the CCl bond of (α-chlorovinyl)silanes to electronically unsaturated transition-metal complex moieties to give vinylidene complexes, e.g. (η6-C6R′6)(CO)2CrCCR2 or MeCp(CO)(L)MnCCR2. With an excess of(α-chlorovinyl)silane, butatriene complexes are formed instead.