Dppe Complexes Research Articles

ChemInform Abstract: An Improved Cobalt Catalyst for Homo Diels-Alder Reactions of Acyclic 1,3-Dienes with Alkynes.

An efficient cobalt(I)-catalysed homo Diels–Alder reaction of acyclic 1,3-dienes and acetylene derivatives is described. The catalyst system consists of a mixture of a readily available CoBr2(dppe) complex, zinc iodide as a cocatalyst, and tetrabutylammonium borohydride as reducing agent. This system increases the reactivity of the cobalt(I) catalyst, so that acyclic dienes and acetylenes can be transformed to the 1,4-dihydroaromatic products in good yield and excellent purity. The regioselectivity of the homo Diels–Alder reaction greatly favours the 1,4-substitution pattern of the formed product.

Metal–heterocyclic thione interactions.: 12. Heterocyclic 2-thiolates of platinum(II) and palladium(II): the crystal structures of first examples of cis-[M( η1- S-pyridine-2-thiolato) 2(L-L)] {M=Pt, Pd, L-L=1,2-bis(diphenylphosphino)ethane; M=Pt, L-L=1,2-bis(diphenylphosphino)ethene} complexes

A series of platinum(II) complexes of stoichiometry cis-[Pt(η 1- S-C 5H 4NS) 2(L-L)] were obtained from the reactions of platinum tetrachloride with pyridine-2-thione (C 5H 5NS) in the presence of Et 3N base in an ethanol–benzene mixture followed by the addition of bis(tertiary phosphines), viz. {Ph 2P–X–PPh 2}, or phosphine chalcogenides {Ph 2P–CH 2–P(E)Ph 2} {X(L-L)=(CH 2) 2(dppe) ( 1), CHCH(dppen) (2), (CH 2) 3(dppp) ( 3), (CH 2) 4(dppb) ( 4), E=S, dppmPS ( 5), E=Se, dppmPSe ( 6)}. Palladium(II) complexes, viz. [Pd(η 1- S-C 5H 4NS) 2(L-L)] {L-L=dppm (X=CH 2) ( 7), dppe ( 8), dppp ( 9), dppmPS ( 10), dppmPSe ( 11)}, were prepared by reacting [PdCl 2(diphosphines)] suspended in ethanol with C 5H 5NS in the presence of aqueous NaOH. All these compounds have been characterised with the help of analytical data [IR, far-IR, NMR ( 1H, 13C, 31P) spectroscopy] and X-ray crystallography (for compounds 1, 2 and 8). The geometry about each metal centre is distorted square planar with trans bond angles of: compound 1, P–Pt–S, 170.31(11), 173.18(10)°; compound 2, P–Pt–S, 168.97(5), 171.43(5)°; compound 8, P–Pd–S, 170.78(8), 171.83(8)°. The bite angles P(1)–M–P(2) and angles trans to bite angles, S(1)–M–S(2), are, respectively: compound 1, 85.68(11), 82.69(11)°; compound 2, 86.65(5), 84.01(6)°; compound 8, 85.19(8), 83.90(7)°. The dppe complexes ( 1 and 8) are isomorphous, monoclinic with space group C2/ c, whereas the dppen complex is triclinic.These compounds represent the first examples of an interesting series of cis-platinum(II) and -palladium(II) derivatives of pyridine-2-thione containing chelating diphosphines and pendant pyridyl groups.

Platinum(II) and palladium(II) saccharinate complexes

A number of platinum(II) and palladium(II) complexes containing the saccharinate ligand (sac −), of the type [MCl(sac)L 2] (M = Pt, L = PPh 3, L 2 = Ph 2PCH 2CH 2PPh 2, dppe; M = Pd, L = PPh 3) have been synthesised by reaction of [MCl 2L 2] with sacNa in methanol. A single crystal X-ray diffraction study carried out on cis-[PtCl(sac)(PPh 3) 2]·4CHCl 3 shows the N-bonded saccharinate and platinum coordination planes to be nearly orthogonal. The results of an electrospray mass spectrometric study of the dppe complex are also reported.

Synthesis of ruthenium vinylidene complexes with dppe ligand and their cyclopropenation reaction

A number of cationic ruthenium vinylidene complexes [Ru]CC(Ph)CH 2R + ([Ru]( η 5-C 5H 5)(dppe)Ru, dppe=Ph 2PCH 2CH 2PPh 2, 5a, R=CN; 5b, R=C 6F 5; 5c, R=Ph; 5d, R= p-C 6H 4CN; 5e, R= p-C 6H 4CF 3; 5f, R=1-C 10H 7; 5g, R=CO 2CH 3) are prepared from electrophilic addition of organic halides to the acetylide complex [Ru]–CCPh at the boiling point of CHCl 3. Complex 5g′, prepared at room temperature, displays similar spectroscopic property as that of 5g but is easily hydrolyzed to give [Ru]COCH 2Ph ( 6). Cyclopropenation of the organic vinylidene moiety of 5a– 5f is accomplished in acetone by deprotonation of 5 with n-Bu 4NOH yielding the neutral cyclopropenyl complexes ( 7a, R=CN; 7b, R=C 6F 5; 7c, R=Ph; 7d, R= p-C 6H 4CN; 7e, R= p-C 6H 4CF 3; 7f, R=1- 10H 7). Protonation of 7b– 7f regenerates the corresponding vinylidene complexes. In the presence of allyl iodide, opening of the three-membered ring of 7a, followed by a subsequent oxidative coupling reaction, gives a dimeric dicationic product {[Ru]CC(Ph)–CHCN} 2 +2 ( 9a). In the processes of preparing the starting material Cp(dppe)RuCl for the acethylide complex, two dppe complexes Ru(dppe) 2Cl 2 ( 2) and [Cp(dppe)RuCl] 2 ( 3) are isolated. Molecular structures of complexes 2, 3, 6, and 7b have been confirmed by X-ray diffraction analysis.

Kinetics of protonation of cis-[FeH2(dppe)2]: formation of the dihydrogen complex trans-[FeH(H2)(dppe)2]+ (dppe = Ph2PCH2CH2PPh2)

Reaction of cis-[FeH2(dppe)2] (dppe = Ph2PCH2CH2PPh2) with acids in tetrahydrofuran solution led to formation of trans-[FeH(H2)(dppe)2]+, although co-ordinated H2 was substituted for N2 or the anion of the acid in a slower process. The kinetics of the initial protonation reaction with several acids has been studied using an electrochemical procedure. The protonations are first order with respect to both the concentrations of the iron complex and the acid, with second-order rate constants (in dm3 mol–1 s–1) at 25 °C of 9.7 × 10–3 (HBF4·Et2O), 1.39 × 10–2 (CF3CO2H), 2.14 × 10–2 (CF3SO3H), 4.8 × 10–2 (HCl) and 1.48 × 10–1 (HBr). The ordering of rate constants within this series of acids is similar to that found for the reactions with cis-[FeH2{P(CH2CH2PPh2)3}]. There is a good correlation between the values of log kHX for the two complexes, which suggests a common mechanism for the formation of dihydrogen complexes in these cases. Kinetic data show that reactions of the dppe complex with all acids are faster than those of the analogous P(CH2CH2PPh2)3 compound. The reaction of cis-[FeH2(dppe)2] with deuteriated acids DX is faster than with HX, and the values of the kinetic isotope effect (k.i.e.), expressed as kHX/kDX, are 0.21 (CF3SO3H), 0.36 (HCl) and 0.55 (HBr). The inverse k.i.e. suggests that protonation occurs through a late transition state, and comparison with cis-[FeH2{P(CH2CH2PPh2)3}] and with theoretical values indicates that protonation of cis-[FeH2(dppe)2] occurs through a transition state closer to the dihydrogen complex than in the case of the related P(CH2CH2PPh2)3 compound.

Platinum group metal complexes of a bis(diphenylphosphino)ethane ligand containing perfluoroalkyl ponytails

The perfluoroalkyl-derivatised bidentate phosphine (4-F13C6C6H4)2PCH2CH2P(C6H4C6F13-4)2 reacted with [PtCl2(MeCN)2], [PdCl2(MeCN)2] or [{RhCl(COD)}2] to yield the complexes [PtCl2(L–L)] 1, [PdCl2(L–L)] 2 and [Pd(L–L)2]2+2Cl– 3 or [{RhCl(L–L)}2] 5 respectively. Complex 3 was reduced with NaBH4 to [Pd(L–L)2] 4 and the chloride bridges in 5 were cleaved with triphenylphosphine to yield [RhCl(L–L)(PPh3)] 6. The reaction of the ligand with [{RhCl2(η5-C5Me5)}2] in a 1∶1 or a 2∶1 ratio yielded either [{RhCl2(η5-C5Me5)}2(L–L)] 7 or, after metathesis with NH4BF4 in acetone, [RhCl(η5-C5Me5)(L–L)]+BF4– 8 respectively. Throughout, spectroscopic studies indicated that the ligand co-ordinates in a similar fashion to bis(diphenylphosphino)ethane (dppe). Complex 7 and the analogous dppe complex are fluxional at room temperature. At the low temperature limit, all the nuclei within these molecules are chemically inequivalent for which simulation suggests a gauche-eclipsed conformation around the PCH2–CH2P bond. Solubility studies indicated that only 4 and 5 are preferentially soluble in perfluorocarbon solvents.

Influence of free and chelating phosphine on the NiS 2P 2 planar chromophore. Synthesis and single crystal structure determination of bis(triphenylphosphine) ( N, N′-iminodiethylenebis(phthalimide)-dithiocarbamato)nickel(II) perchlorate, methanol and water solvate and [1,2-bis(diphenylphosphino- k. P, P′)ethane]-( N, N′-iminodiethylenebis(phthalimide)dithiocarbamato)nickel(II) tetraphenylborate water solvate

Syntheses and crystal structures of [Ni(padtc) (PPh 3) 2]ClO 4∗dCH 3OH∗dH 2O ( 1) and [Ni(padtc)(dppe)] BPh 4∗dH 2O (2) (padtc = N, N′-iminodiethylenebis(phthalimide)dithiocarbamate, dppe = 1,2-bis(diphenylphosphino)ethane) are reported. Crystal parameters: complex 1, space group P2/n, a = 26.388(3), b = 12.862(4), c = 17.815(2) A ̊ , β = 106.03(3)°, V = 5811.3(2) a ̊ A 3, Z = 4, R = 0.067 for 4150 reflections with I>2 σ( I); complex 2, space group P2 1/c, a = 19.722(2), b = 34.931(3), c = 20.373(3) A ̊ , β = 114.54(3)°, V = 12767.4(4) A ̊ 3, Z = 8, R = 0.069 for 12 012 reflections with I>2 σ( I). The bulky dithiocarbamate padtc is an umbrella shaped molecule flanking the NiS 2P 2 chromophore. Complex 2 is a molecule with the chelating phosphine dppe. Both the complexes have planar NiS 2P 2 chromophores in keeping with the observed diamagnetism. A relatively short NiP distance is observed in the dppe complex 2. The chelating dppe forces the NiS distances to be symmetric (2.200(2), 2.204(2) Å) unlike PPh 3 which induces asymmetry (2.227(3), 2.198(2) Å). Shortening of the thioureide CN bonds (1.307(10) Å in 1, 1.323(7) Å in 2, 1.359(3) Å in free padtc −) in the complexes is a clear indication of the localisation of the nitrogen electrons between C and N. Thioureide stretching bands in Ni(padtc) 2, [Ni(padtc)(PPh 3) 2] + and [Ni(padtc)(dppe)] + occur at 1494, 1509 and 1512 cm −1, respectively, in keeping with the significant reduction in CN bond distances.

2,6-Diisopropylphenylimido and diphenylacetylene complexes of tungsten containing the bidentate ligands 4,4′-dimethyl-2,2′-bipyridine and 1,2-bis(diphenylphosphino)ethane

Sodium–mercury amalgam reduction of [{WCl4(NC6H3Pri2-2,6)}2] in the presence of 4,4′-dimethyl-2,2′-bipyridine (dmbipy) or 1,2-bis(diphenylphosphino)ethane (dppe) gave the d1 complexes [WCl3(NC6H3Pri2-2,6)(dmbipy)]1 and [WCl3(NC6H3Pri2-2,6)(dppe)]2. A crystal-structure determination of complex 2 shows the three chloro ligands in a mer arrangement and the dppe ligand phosphorus atoms lying trans to one chloro ligand and also the imido ligand. The W–P bond trans to the chloro ligand is normal [2.550(2)A] whereas the W–P bond trans to the imido ligand is very long [2.765(2)A]. One phenyl group of dppe rotates to accommodate an isopropyl group of the imido ligand. Sodium–mercury amalgam reduction of [{WCl4(PhC2Ph)}2] in the presence of dmbipy gave [WCl3(PhC2Ph)(dmbipy)] which the W–Cl stretches suggest is the mer trichloride. However, an IR spectrum of the product of standing [{WCl4(PhC2Ph)}2] and dmbipy in tetrahydrofuran indicates the fac isomer. A reduction of [{WCl4(PhC2Ph)}2] in the presence of dppe gave [WCl3(PhC2Ph)(dppe)] for which the mer isomer is preferred. The dppe complexes do not give characterisable complexes on further reduction in the presence of diphenylacetylene, ethylene or CO. Sodium mercury amalgam reduction of 1 in the presence of diphenylacetylene gave [WCl2(NC6H3Pri2-2,6)(PhC2Ph)(dmbipy)] which IR and NMR spectra indicate has an asymmetric structure where the alkyne ligand is a two-electron donor. Reductions of complex 1 under ethylene or CO gave [WCl2(NC6H3Pri2-2,6)(CH2CH2)(dmbipy)] and [WCl2(NC6H3Pri2-2,6)(CO)(dmbipy)] both of which consist of several isomers.

Mono- and bis-diazenido complexes of rhenium(III) containing bidentate ditertiary phosphine ligands. The crystal and molecular structures of [Re(NNC6H4Me-4)2(Ph2PCH2CH2PPh2)2][PF6]·2dmf, [Re(NNC6H4Cl-4)2(Me2PCH2CH2PMe2)2][PF6] and [ReCl(NNC6H4Me-4)(Me2PCH2CH2PMe2)2][PF6

Reaction of the ReIII bis-diazenido starting materials [ReCl(NNC6H4X-4)2(PPh3)2](X = Cl 1 or Me 2) with excess dppe (Ph2PCH2CH2PPh2) in methanol–toluene under reflux gave the novel orange-brown, formally 20-electron ReIII bis-diazenido cations [Re(NNC6H4X-4)2(dppe)2]+(X = Cl or Me) in good yield by addition of a suitable anion to the cooled reaction mixture. Reaction of 1 and 2 with the more reducing dmpe (Me2PCH2CH2PMe2) ligand gave the formally 20-electron bis-diazenido cation [Re(NNC6H4X-4)2(dmpe)2]+ for X = Cl but the 18-electron mono-diazenido cation [ReCl(NNC6H4X-4)(dmpe)2]+ for X = Me. The structures of complexes [Re(NNC6H4Me-4)2(dppe)2][PF6]·2dmf (dmf = dimethylformamide)5, [Re(NNC6H4Cl-4)2(dmpe)2][PF6]6 and [ReCl(NNC6H4Me-4)(dmpe)2][PF6]7 have been determined: 5, triclinic, space group P, a= 13.046(3), b= 13.250(3), c= 12.233(4)A, α= 110.74(2), β= 95.86(2), γ= 115.83(2)°, Z= 1, R= 0.040; 6 monoclinic, space group P21/c, a= 8.992(2), b= 21.947(2), c= 18.982(2)A, β= 91.45(1)°, Z= 4, R= 0.056; 7 orthorhombic, space group Pnma, a= 19.298(2), b= 11.327(2), c= 13.960(2)A, α=β=γ= 90°, Z= 4, R= 0.042. All three complexes have pseudo-octahedral co-ordination with four P donors in a planar equatorial array. The M–N–N angle of the diazenide ligands is found to be dependent on the steric requirements of the diphosphine ligands, the smaller dmpe ligand permitting the M–N–N angles in 6 to decrease to 147.3(5) and 149.0(4)° compared to values of around 162.7(2)° for the dppe complex 5. Reaction of [NH4][ReO4] with the arylhydrazine hydrochloride 4-MeC6H4NHNH2·HCl in CH2Cl2 in the presence of SiMe3Cl and pyridine (py) gave the new hydrazide [ReCl3{NN(SiMe3)C6H4Me-4}2(py)]. Subsequent reaction with PPh3 in MeOH gave the ReIII diazenide [Re(OMe)(NNC6H4Me-4)2(PPh3)2], and overall this provides a route for the synthesis of Re diazenides directly from perrhenate.

Nickel(II) bis(phosphine) complexes

The synthesis, characterization, disproportionation, and dynamic ligand-exchange reactions of the complexes [Ni II (P-P)X 2 ], where P-P is dppe, dppey and X=Cl, Br, I, and [Ni II (P-P) 2 ]X 2 , where X=I or NO 3 , are reported. For [Ni II (P-P)X 2 ] the halide affinity in chloroform was determined to be Cl>Br>I by 31 P NMR spectroscopy, and dppey complexes were more stable than dppe complexes. Disproportionation reactions, 2[Ni(dppe)X 2 ]⇄[Ni(dppe) 2 ]X+NiX 2 , occurred readily in methanol and less so in chloroform, followed by phosphine oxidation

Synthesis of some cationic 16- and 18-electron nickel alkyl phosphine complexes containing bidentate ligands: ligand-dependent square-planar, trigonal-bipyramidal, and square-pyramidal co-ordination geometries, their reactions with CO and alkynes, and the crystal structure of [Ni(CH2SiMe3)(PMe3)3]BF4

Treatment of [NiMe(PMe3)4]BF4(1) with chelating ligands L–L gives the complexes [NiMe(PMe3)2(L–L)]BF4 which may be rigid, with a trigonal-bipyramidal 18-electron structure [L–L = 2,2′-bipyridyl (bipy) or 1,10-phenanthroline (phen)], or show fluxional behaviour [L–L = 1,2-bis(diphenylphosphino)ethane (dppe) or 1,2-bis(dimethylphosphino)ethane (dmpe)].The latter two complexes are in equilibrium with square-planar [NiMe(PMe3)(L–L)]BF4. Treatment of (1) with excess of dmpe leads to complete substitution of PMe3 to give square-pyramidal [NiMe(dmpe)2BF4. In [Ni(CH2SiMe3)(PMe3)3]BF4(9) the co-ordination of a fourth PMe3 ligand to give a five-co-ordinate complex analogous to (1) is precluded for steric reasons. The crystal structure of (9) shows the metal centre in a tetrahedrally distorted square-planar environment, with P–Ni–P and P–Ni–C angles of 135.5(2) and 157.8(7)°, respectively. While [NiMe(PMe3)2(dmpe)]BF4 and [NiMe(dmpe)2]BF4 react with CO to give stable nickel acyl complexes, the dppe complex [Ni(COMe)(PMe3)(dppe)]BF4 is only observed at low temperature. Treatment of (1) with 2 equivalents of PPh3 or with an excess of bipy, phen, or dppe leads to reductive elimination and formation of zerovalent nickel complexes. Similarly, PhCCPh induces the reductive methyl migration in (1) from nickel to PMe3via spectroscopically observable ylidic intermediates to give [Ni(C2Ph2)(PMe3)2] and [PMe4]BF4.

Spectroscopic investigations on the structure and fluxionality of the trihaptocycloheptatrienyl complexes [MX(CO) 2(LL)(η 3-C 7H 7)] (M  Mo, W; X  I, Cl; LL  bisphosphine or diamine) and synthesis of the tetracyanoethene adducts [WI(CO) 2{Ph 2P(CH 2) nPPh 2}{η 3-C 9H 7(CN) 4}] ( n = 1 or 2)

Spectroscopic investigations, including 31P, 1H and 13C NMR studies, on the formally 6-coordinate bisphosphine complexes [MX(CO) 2{Ph 2P(CH 2) n PPh 2}(η 3-C 7H 7)] (M  Mo, W; X  I, Cl; n = 2 (dppe), n = 1 (dppm); C 7H 7  cycloheptatrienyl) reveal a structure with no molecular plane of symmetry in which inequivalent P-donor atoms are arranged cis-cis and cis-trans to the two mutually cis-carbonyl groups. The dppe complexes exhibit a fluxional process which interconverts inequivalent phosphorus environments. Low temperature 1H and 13C NMR studies on the diamine derivatives [MCl(CO) 2(H 2NCH 2CH 2NH 2)(η 3-R)] (M  Mo, W, R  C 7H 7; M  Mo, R  C 3H 5 (allyl)) imply that the non-symmetric structure of the bisphosphine analogues is adopted. The adducts [WI(CO) 2{Ph 2P(CH 2) n -PPh 2} {η 3-C 9H 7(CN) 4}] ( n = 1 or 2) are formed by tetracyanoethene addition to the trihapto-bonded cycloheptatrienyl ring of the tungsten complexes [WI(CO) 2-{Ph 2P(CH 2) n PPh 2}(η 3-C 7H 7)] ( n = 1 or 2).

ChemInform Abstract: 31P NMR Studies of cis‐(RhCl(CO)(bis‐phosphine)) Complexes

Abstract Further examples of complexes with the previously unique ci s-chelated [RhCl(CO)(bis-phosphine)] structure are reported where bis-phosphine=R 2 P- (C 2 B 10 H 10 )PR′ 2 with R and R′=C 6 H 5 or NMe 2 . In the unsymmetrical R ≠ R′ example only the isomer with PPh 2 trans to Cl is formed. These complexes as well as the analogous dppe complex show interesting fluxional behavior under CO implying the existence of a five-coordinate [RhCl(CO) 2 (bis-phosphine)] species. The compound trans -[RhCl(CO){Ph 2 P(C 2 B 10 H 10 )H} 2 ] is also described.

Cyclopentadienylruthenium complexes with sulphur donor ligands: II. A comparative study of the reactivity of Ru(η-RC 5H 4)Cl(L) 2 (R = H, CH 3, CH 3CO; L = CO, Ph 2PCH 2CH 2PPh 2/2, P(CH 2CH 2CN) 3) towards anionic (SS) donor ligands

The complexes Ru(η-RC 5H 4)Cl(PPh 3) 2 (R = H, CH 3, CH 3CO) readily react with the tertiary phosphines Ph 2PCH 2CH 2PPh 2 (dppe) and P(CH 2CH 2CN) 3 (tcep) to give Ru(η-RC 5H 4)Cl(dppe) and Ru(η-RC 5H 4)Cl(tceP) 2 (R = H, CH 3, CH 3CO). The dppe complex with R = CH 3 reacts with (S 2COR′) − ions to give Ru(η-CH 3C 5H 4)(S 2COR′)(dppe) (R′ = Me, Et) involving monodentate coordination of the dithiolate, and with (S 2CNR′ 2) - ions to give Ru(S 2CNR′ 2) 2(dppe)(R′ = Et). The tcep complexes do not react with the dithiolates under these conditions. The reaction of Ru(η-C 5H 5)Cl(CO) 2 with KS 2COEt has also been studied.

31P NMR studies of cis-[RhCl(CO)(bis-phosphine)] complexes

Further examples of complexes with the previously unique cis-chelated [RhCl(CO)(bis-phosphine)] structure are reported where bis-phosphine=R 2P- (C 2B 10H 10)PR′ 2 with R and R′=C 6H 5 or NMe 2. In the unsymmetrical R ≠ R′ example only the isomer with PPh 2 trans to Cl is formed. These complexes as well as the analogous dppe complex show interesting fluxional behavior under CO implying the existence of a five-coordinate [RhCl(CO) 2(bis-phosphine)] species. The compound trans-[RhCl(CO){Ph 2P(C 2B 10H 10)H} 2] is also described.

Studies on licand displacement of thiourea in technetium/III/-coordination compounds by chlorine and 1,2 bis/diphenylphosphino/-ethane /dppe/

Ligand displacement reaction between Tc/III/-thiourea complexes and the model ligand 1,2 bis/diphenylphosphino/ ethane /dppe/ were investigated. The results appear unfavourable to the purpose of synthesizing Tc/III/ dppe complexes.

Preparation, Resolution, and Spectroscopic Properties of Bis[(2-aminoethyl)diphenylphosphine]- and (Ethylenediamine)[1,2-bis(diphenylphosphino)ethane]–Cobalt(III) Complexes of Acetylacetonate, Malonate, Oxalate, and Carbonate Ion

Abstract New complexes of the [Co(O–O)(edpp)2]- and [Co(O–O)(en)(dppe)]- type were prepared from trans(Cl, Cl)[CoCl2(edpp)2]ClO4 and trans-[CoCl2(en)(dppe)]ClO4·H2O, respectively, where O–O is an acetylacetonate, malonate, oxalate, or carbonate ion, and en, edpp, and dppe denote ethylenediamine, (2-aminoethyl)diphenylphosphine, and 1,2-bis(diphenylphosphino)ethane, respectively. All the complexes of the former type gave two geometrical isomers of trans(P, P) and trans(P, N) configurations, which were assigned on the basis of the 1H and 3C NMR, and electronic absorption spectra. No trans(N, N) isomers were formed. The yields of the trans(P, N) isomers were always larger than those of the corresponding trans(P, P) isomers. With the decreasing ring members of the O–O chelates, the yield of the trans(P,P) isomer decreases, the trans(P,P)-carbonato complex being formed in trace amounts. The first absorption bands of the trans(P,P) isomers have very strong intensity as compared with those of the corresponding trans(P,N) and the dppe complexes. All the complexes except for [Co(O–O)(en)(dppe)]+ (O–O=malonate and oxalate ions) were resolved by the chemical or SP-Sephadex C-25 column chromatographic method, and the circular dichroism spectra were recorded and compared with those of related complexes.

Oxidative addition and insertion reactions of cyclic alkyne-platinum(0) complexes

The reactions of various alkyne-platinum(0) complexes with methyl iodide and with iodine have been studied. The 3-hexyne complex Pt(C 2H 5C 2C 2H 5)(PPh 3) 2 gives alkyne-free oxidative addition products PtI(CH 3) (PPh 3) 2 and PtI 2 (PPh 3) 2 exclusively. In contrast, the strained cyclic alkyne complexes Pt(C 6H 8)(PPh 3) 2, Pt(C 7H 10)(PPh 3) 2, Pt(C 6H 8) (dppe) and Pt(C 7H 10) (dppe) 1 1 C 6H 8 = cyclohexyne; C 7H 10 = cycloheptyne; dppe = 1,2-bis (diphenylphosphino)ethane, Ph 2PCH 2CH 2PPh 2 react with methyl iodide to give mainly 2-methylcycloalkenyiplatinum(II) complexes, e.g. PtI(C 6H 8CH 3) (PPh 3) 2, formed by electrophilic attack on the metal-alkyne bond. Iodine reacts similarly with Pt(C 6H 8) (PPh 3) 2 and Pt(C 7H 10) (PPh 3) 2 to give 2-iodocycloalkenylplatinum(II) complexes but, in the case of the corresponding dppe complexes, PtI 2(dppe) is the main product. The insertion reaction of methyl iodide with Pt(C 6H 8)(PPh 3) 2 proceeds via an oxidative addition intermediate PtI(CH 3) (C 6H 8) (PPh 3) 2 which can be isolated. Trifluoromethyl iodide reacts with Pt(C 6H 8)(PPh 3) 2 to give a 2-iodocyclohexenyl complex Pt(CF 3) (C 6H 8I) (PPh 3) 2 and with Pt(C 7H 10) (PPh 3) 2 to give PtI(CF 3) (PPh 3) 2. 31P NMR data are given and discussed.