SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF (8)(ETA(1)-PH)(MU(4)-ETA(3)-PHPC(H)CPH)(MU-PPH2)], WITH A ETA(1)-PHENYL GROUP ARISING FROM SELECTIVE CLEAVAGE OF A COORDINATED PH2PC(H)CPH LIGAND, AND OF THE CO-INSERTED PRODUCT (ETA(1)-C(O)PH)(MU(4)-ETA(3)-PHPC(H)CPH)(MU-PPH2)]

The Ph2PC(H)CPh ligand in [Ir-4(Co)(9)(mu(3)-eta(3)-Ph2PC(H)CPh)(mu-PP h2)] (1) undergoes selective P-C bond scission upon thermolysis in tol uene at 70 degrees C, to give (8)(eta(1)-Ph)(mu(4)-eta(3)-PhPC-(H)CPh) (mu-PPh2)] (2; 60%), in addition to unreacted 1. P-31{H-1}, C-13{H-1}, and H-1 NMR studies indicated the presence of two isomers in solution in a 3.2:1 ratio. The minor isomer 2b was fully characterized by sing le-crystal X-ray diffraction and exhibits a flat butterfly of metal at oms, with the PhPC(H)CPh ligand interacting with all four Ir atoms. Th e eta(1)-Ph ligand is located on a wingtip Ir, on a radial site, trans to an Ir-Ir bond and cis to the P of the vinylidene ligand. A structu re was proposed for the major isomer 2a, on the basis of multinuclear NMR spectroscopy, in which the eta(1)-Ph ligand is located on an axial site, traits to the P of the vinylidene ligand. VT (31){H-1} NMR (25- 90 degrees C) did not show interconversion of 2a and 2b. Carbonylation of the mixture of the two isomers yielded the CO inserted-products 3a and 3b (1:1.3), together with unreacted 2a. The molecular structure o f [Ir-4- (eta(1)-C(O)Ph)(mu(3)-eta(3)-PhPC(H)CPh)(mu-PPh2)] (isomer 3b ), established by an X-ray analysis, is similar to that of 2b, except for the acyl group that remains bound to the same Ir atom but occupies the neighboring radial site. Multinuclear NMR studies showed that the eta(1)-C(O)Ph group in isomer 3a occupies the same axial position as eta(1)-Ph in 2a. A mechanism involving migration of the eta(1)-Ph grou p in 2a and 2b, upon carbonylation, to give 3b and 3a, respectively, h as been proposed.