No abstract

The ethene derivatives [(eta(5)-C(5)R(5))RuX(C(2)H(4))(PPh(3))] with R=H and Me, which have been prepared from the eta(3)-allylic compounds [(eta(5)-C(5)R(5))Ru(eta(3)-2-MeC(3)H(4))(PPh(3))] (1, 2) and acids HX under an ethene atmosphere, are excellent starting materials for the synthesis of a series of new halfsandwich-type ruthenium(II) complexes. The olefinic ligand is replaced not only by CO and pyridine, but also by internal and terminal alkynes to give (for X=Cl) alkyne, vinylidene, and allene compounds of the general composition [(eta(5)-C(5)R(5))RuCl(L)(PPh(3))] with L=C(2)(CO(2)Me)(2), Me(3)SiC(2)CO(2)Et, C=CHCO(2)R, and C(3)H(4). The allenylidene complex [(eta(5)-C(5)H(5))RuCl(=C=C=CPh(2))(PPh(3))] is directly accessible from 1 (R=H) in two steps with the propargylic alcohol HC triple bond CC(OH)Ph(2) as the precursor. The reactions of the ethene derivatives [(eta(5)-C(5)H(5))RuX(C(2)H(4))(PPh(3))] (X=Cl, CF(3)CO(2)) with diazo compounds RR'CN(2) yield the corresponding carbene complexes [(eta(5)-C(5)R(5))RuX(=CRR')(PPh(3))], while with ethyl diazoacetate (for X=Cl) the diethyl maleate compound [(eta(5)-C(5)H(5))RuCl[eta(2)-Z-C(2)H(2)(CO(2)Et)(2)](PPh(3))] is obtained. Halfsandwich-type ruthenium(II) complexes [(eta(5)-C(5)R(5))RuCl(=CHR')(PPh(3))] with secondary carbenes as ligands, as well as cationic species [(eta(5)-C(5)H(5))Ru(=CPh(2))(L)(PPh(3))]X with L=CO and CNtBu and X=AlCl(4) and PF(6), have also been prepared. The neutral compounds [(eta(5)-C(5)H(5))RuCl(=CRR')(PPh(3))] react with phenyllithium, methyllithium, and the vinyl Grignard reagent CH(2)=CHMgBr by displacement of the chloride and subsequent C-C coupling to generate halfsandwich-type ruthenium(II) complexes with eta(3)-benzyl, eta(3)-allyl, and substituted olefins as ligands. Protolytic cleavage of the metal-allylic bond in [(eta(5)-C(5)H(5))Ru(eta(3)-CH(2)CHCR(2))(PPh(3))] with acetic acid affords the corresponding olefins R(2)C=CHCH(3). The by-product of this process is the acetato derivative [(eta(5)-C(5)H(5))Ru(kappa(2)-O(2)CCH(3))(PPh(3))], which can be reconverted to the carbene complexes [(eta(5)-C(5)H(5))RuCl(=CR(2))(PPh(3))] in a one-pot reaction with R(2)CN(2) and Et(3)NHCl.

In contrast to the large number of vinylidene and allenylidene transition-metal complexes containing a linear MdCdC or MdCdCdC fragment, 1 related compounds with a MC 4 or MC 5 unit are still quite rare. Recently, Dixneuf et al. described the synthesis of a cationic ruthenium complex of composition [RuCl-(dCdCdCdCdCPh 2 )(dppe) 2 ] + (dppe ) Ph 2 PCH 2 CH 2 -PPh 2 ), 2 and shortly thereafter we reported the isolation and structural characterization of the first neutral species trans-[IrCl(dCdCdCdCdCPh 2 )(PiPr 3 ) 2 ], having a linear MC 5 chain. 3 In the meantime, a paper describing the preparation of the corresponding octahedral derivatives [M(dCdCdCdCdC(NMe 2 ) 2 )(CO) 5 ] (M ) Cr, W) has also appeared. 4 The unexpected thermodynamic stability of the IrC 5 complex prompted us to prepare also the analogous RhC 5 compound trans-[RhCl(dCdCdCdCdCPh 2 )(Pi-Pr 3 ) 2 ] (6) with the particular aim of comparing the reactivity of this metallacumulene with that of the structurally similar RhC 3 species trans-[RhCl(dCdCd CPh 2 )(PiPr 3 ) 2 ]. 5 The methodology to obtain 6 is outlined in Scheme 1. Treatment of the labile dimer 1 6 with the substituted pentadiyne HCtCCtCCPh 2 OSiMe 3 7 in pentane at -78°C afforded, after warming up to room temperature, the π-alkyne complex 2 as an orange solid in 63% yield. 8,9 The couplings of the CtCH proton and of the respective alkyne carbon atoms to 103 Rh support the assumption that it is the terminal triple bond which is coordinated to the metal center.Thermal rearrangement of 2 in toluene, which was carefully monitored by 31 P NMR spectroscopy, gave first (20) Armitage, J. B.; Jones, E. R. H.; Whiting, M. C.

A series of (diazoalkane)rhodium(I) compounds of the general composition trans-[RhCl(N2CRR‘)(PiPr3)2] with R = R‘ = Ph, p-C6H4Me, p-C6H4Cl and R = Ph, R‘ = p-C6H4Me, o-C6H4Me, CH3, CH2Ph, CF3 has been prepared from the dimer [RhCl(PiPr3)2]2 (1) and the diazoalkane. This preparative route has also been extended to complexes in which the N2C unit(s) of 1,4-C6H4{C(Ph)N2}2, 9-diazofluorene, 9,10-anthraquinone-9-diazide, and 3-methyl-1,4-naphthoquinone-1-diazide is (are) linked to a 14-electron [RhCl(PiPr3)2] fragment. While C(CO2Et)2N2 behaves as expected and affords upon treatment with 1 the complex trans-[RhCl{N2C(CO2Et)2}(PiPr3)2), CH(CO2Et)N2 reacts with the same starting material to give the dinitrogen derivative trans-[RhCl(N2)(PiPr3)2] (12). The reactions of trans-[RhCl(C2H4)(PiPr3)2] (2) with both N2CC4Cl4 and N2CC4Ph4 afford trans-[RhCl(N2CC4X4)(PiPr3)2] (X = Cl, Ph), and the same type of ligand exchange takes place by treatment of trans-[RhCl(C2H4)(SbiPr3)2] with N2CC4Cl4. The reactions of trans-[RhCl(N2CRR‘)(PiPr3)2] (3−7, where R and R‘ are aryl) with excess ethene give, instead of a disubstituted cyclopropane, exclusively the trisubstituted olefin CH3CHCRR‘. The reaction of 1 with PhC(R)NNH2 (R = Ph, Me) proceeds mainly by orthometalation to yield the six-coordinate rhodium(III) complexes [Rh(H)Cl{κ2-C,N-C6H4C(NNH2)R}(PiPr3)2]; of these, that with R = Ph reacts with Al2O3 to give trans-[RhCl(N2CPh2)(PiPr3)2] and 12. The alkynylrhodium(I) derivatives trans-[Rh(C⋮CX)(C2H4)(PiPr3)2] (X = H, tBu) behave similarly to 2 and afford upon treatment with Ph2CN2 and C12H8CN2 the corresponding diazoalkane compounds trans-[Rh(C⋮CX)(N2CRR‘)(PiPr3)2] by ligand exchange. The reaction of 2 with the diazo ketones RC(O)C(Ph)N2 (R = Ph, Me) leads to complexes of the general composition [RhCl{N2C(Ph)C(O)Ph}(PiPr3)2], in which the diazo ketone is probably coordinated in a chelating fashion to the metal center. The keto ester derivative (CH3)2CHCH2CH2C(O)C(CO2Me)N2 reacts with 2 to give a mixture of two isomers, one of which could be separated by fractional crystallization. The supposed chelating bonding mode of the diazo ligand in this compound via the terminal nitrogen and the keto oxygen could be confirmed by an X-ray crystal structure analysis.

The mixed-ligand complex [IrCl(C2H4)(SbiPr3)(PiPr3)] (2), prepared from [IrCl(C2H4)(PiPr3)]2 (1) and SbiPr3, reacts not only with CO, diphenylacetylene, and H2 by ligand substitution or oxidative addition but also with diaryldiazomethanes R2CN2 to give the four-coordinate iridium(I) carbenes [IrCl(CR2)(SbiPr3)(PiPr3)] (8−10) in 60−70% isolated yield. In contrast, treatment of 2 and of the related cyclooctene derivative trans-[IrCl(C8H14)(SbiPr3)2] (12) with C5Cl4N2 affords the diazoalkane complexes trans-[IrCl(N2C5Cl4)(SbiPr3)(EiPr3)] (11, E = P; 13, E = Sb) without elimination of N2. Displacement of the stibine ligand in 8−10 by PiPr3 leads to the corresponding bis(phosphine) compounds trans-[IrCl(CR2)(PiPr3)2] (14−16), while the reaction of 8 (R = C6H5) with NaC5H5 yields the half-sandwich-type complex [(η5-C5H5)Ir(CPh2)(PiPr3)] (17). Protonation of 17 with HCl occurs stepwise to give via the iridium(III) alkyl [(η5-C5H5)IrCl(CHPh2)(PiPr3)] (20) the ring-substituted isomer [(η5-C5H4CHPh2)IrHCl(PiPr3)] (21); however, if 17 is treated with HBF4, a cationic complex is formed which probably contains a η3-coordinated benzylic ligand. The square-planar iridium(I) carbenes 8 and 14 react with HBX4 (X = F, ArF) to afford the ionic products [IrHCl(CPh2)(PiPr3)(EiPr3)]BX4 (23, 24, E = P; 25, E = Sb) and with HCl to give the relatively labile octahedral species [IrHCl2(CPh2)(PiPr3)(EiPr3)] (26, E = P; 27, E = Sb). Treatment of 8 and 14 with ethene yields, besides [IrCl(C2H4)2(SbiPr3)2] (18) and/or trans-[IrCl(C2H4)(PiPr3)2] (28), a mixture of two isomeric olefinic products CH2CHCHPh2 (29) and CH3CHCPh2 (30), the ratio of which is independent of the ligand sphere of the iridium precursor. The molecular structures of 13, 14, 17, and 24 have been determined by X-ray crystallography.