No abstract

No abstract

The thermal conversion of [Os,(CO),,(PRPh,)] (R = M e or Ph) into [Os3(p3-C,H,)(p3-PR)(CO),] (3) by loss of carbon monoxide, and probably benzene, has been reported. By carrying out the reactions at lower temperatures we have been able to isolate [Os,(p-H) (p,-C,H,PMePh) (CO),] (1 a) and [Os,(p,-C,H,PMe) (CO),,] (2a) from the methyldiphenylphosphine compound and corresponding derivatives (1 b) and (2b) from the triphenylphosphine derivative. Both (1) and (2) convert thermally to the p3-C,H, clusters (3) and are deduced to be intermediates in the formation of (3). The single-crystal X-ray structures of (1 a) and (2a) are reported. In (1 a), p,-C,H,PMePh-o is a five-electron donor bonded through P t o one 0 s atom, by a a-Os-C bond to another, and by an q2 interaction of the C, H, ring to the third. Compound (2a) contains the p3 ligand C,H,PMe-o, as a four-electron donor, and a bridging CO ligand. In the degradation of PRPh, into the components C, H, , PR, and C,H,, ortho-metallation is the first step, but probably follows an initial loss of co. The loss of CO on heating [Os,(CO),,] to give unsaturated species is followed by the making of Os-0s bonds and the formation of higher clusters such as [os6(co)l~]~' On the other hand, decarbonylation of [Os,(CO), ,L], where L is a tertiary phosphine or arsine, generally leads to bond cleavages (internal oxidative additions) within the ligands L. Two C-H bonds of PMe, are cleaved in the formation of [Os,H,(p,-Me,PCH)-(CO),] from [Os,(CO) , , (PMe,)] ' while the corresponding double decarbonylation of [Os,(CO) ,(PMe,Ph)] leads to one aryl C-H and one aryl C-P cleavage to give [Os3H(p3-C6H4)-(p-PMe,)(CO),] and the PMe, group remains intact.'*' More extensive breakdown occurs in decarbonylation of the remaining members of the series, [Os,(CO),,L] (L = PMePh, or PPh,), which give [oS3(p~-c~H4)(~3-PR)(co)g] (R = Me or Ph).5 Two C-P bonds and an aryl C-H bond are cleaved and, since benzene is probably the by-product, a C-H bond is also formed. These studies on the series PMe,-,Ph, (x = 0-3) show that aryl C-H cleavage is more favourable than methyl C-H cleavage but it is not clear whether ortho-metallation occurs or P-C(ary1) bonds are cleaved in the step immediately following loss of CO from the the PMe,Ph, PMePh,, or PPh, complexes. By isolating and structurally characterising two intermediates in the degradation of [Os,(CO), l(PMePh,)] we have mapped out the main features of the route to [OS&-C6H4)(p3-PMe)(C0)91.

No abstract

parallel phenyl rings leading to 1H n.m.r. (phenyl) resonances as high-field as 6 5.7.Unexplained features of n.m.r. spectra of several transoctahedral complexes containing four PMe2Ph ligands in a plane have been described.1-3 A broad 1H n.m.r. Me singlet at room temperature has been reported for trans-[IrC12(P-Me2Ph),]+ (1)1 and one PMe2Ph ligand in the isoelectronic trans-[OsC12(PMe2Ph)4] was thought to be unique, possibly co-ordinated through the phenyl group agostically or by n-complexation? We now show that the Ir complex contains four M-P bonds and that the n.m.r. effects result from the presence of rotamers in exchange, each containing at least two phenyl groups in close parallel alignment. The complexes trans-[IrC12(EMe2Ph)4][C104], (1, E = P) and (2, E = As) were prepared as yellow crystals by treating trans, rner-[IrC12(H20)(EMe2Ph)3][C104]4 with EMe2Ph. The single-crystal X-ray structure of (1) (Figure l)t shows that two ~ t Crystal data for compound (1): C32H44C131r04P4, M = 915.19, monoclinic, space group n 1 / c , a = 11.185(2), b = 26.301(2), c =