VINYLIDENE TRANSITION-METAL COMPLEXES .38. ALKYNE, ALKYNYL, VINYLIDENE, ALLENYLIDENE AND BENZYL RHODIUM COMPLEXES WITH THE PHOSPHINO ETHER IPR(2)PCH(2)CH(2)OME AS A MONODENTATE AND BIDENTATE LIGAND

The monomeric four-coordinate rhodium(I) compound [RhClL(2)] (L=(i)Pr(2)PCH(2)CH(2)OMe()) (1) reacts with terminal alkynes HC=CR (R=(t)Bu, Tol, CH(Ph)OH, C(Ph)(2)OH, C(Pr-i)(2)OH, C(Me)(2)OH) to give the vinylidene complexes trans-[RhCl(=C=CHR)L(2)] (5-10) as the final products. Whereas for R=C(Ph)(2)OH, the stepwise conversion of the initially formed square-planar alkyne derivative 2 to the octahedral alkynyl(hydrido)compound 3 and further to the vinylidene complex 5 has been confirmed, for R=C(Pr-i)(2)OH a complete rearrangement of the isolated compound [RhH(C=CR)Cl(kappa(P)-L)(kappa(2)(P,O)-L)] (4) to the vinylidenerhodium isomer 6 could not be achieved. The abstraction of water from 10 (R=C(Me)(2)OH) induced by catalytic amounts of CF3CO2H leads to the formation of the vinylvinylidenerhodium(I) compound trans-[RhCl(=C=CHC(Me)=CH2)L(2)] (11); in contrast, the corresponding reaction of 5 (R=C(Ph)(2)OH) with acidic Al2O3, yields the allenylidene complex trans-[RhCl(=C=C=CPh(2))L(2)] (12). The eta(3)-benzylrhodium(I) compounds [Rh(eta(3)-CH2C6H4-4-R)L(2)] (14, 15), which are prepared from 1 and Grignard reagents 4-RC(6)H(4)CH(2)MgCl (R=H, CH3), react with CO to give the eta(1)-benzyl derivatives [Rh(eta(1)-CH2C6H4-4-R)(CO)L(2)] (16, 17). The reaction of 14 with HC=CC(Pr-i)(2)OH yields the bis(alkynyl)hydridorhodium(III) compound [RhH(C=CR)(2)L(2)] (R=C(Pr-i)(2)OH) (20), the structure of which has been determined by X-ray crystallography. While compound 14 reacts with HC=CC(Me)(2)OH under an ethene atmosphere to give trans-[Rh(C=C-C(Me)(2)OH)(C2H4)L(2)] (21), on treatment of 14 with HC=CTol in the presence of HBF, the cationic complex [RhL(2)]BF4 (22a) is obtained. The corresponding PF6 salt 22b is prepared from [Rh(C8H14)(2)(OCMe(2))(2)]PF6 and L.