Mono- and dinuclear rhodium(I) and rhodium(III) complexes with the bulky phosphine 2,6-Me2C6H3CH2CH2PtBu2, including the first structurally characterized cis-configurated dicarbonyl compound, cis-[RhCl(CO)2(PR3)]

The bulky functionalized phosphine 2,6-Me2C6H3CH2CH2PtBU2 (3) was prepared in a stepwise fashion from the Grignard reagent 2,6-Me2C6H3CH2CH2MgCl, tBUPCl(2), and tBuLi. Phosphine 3 reacts with the olefin compounds [RhCI(C2H4)(2)](2) and [RhCl(C8H14)(2)](2) to give the substitution products [RhCl(olefin)(3)](2) (8, 9), of which 9 (olefin = C2H4) has been characterized crystallographically. While 9 is rather inert toward 3, it reacts with 3 under a hydrogen atmosphere to give the dihydrido complex [RhH2Cl(3)(2)] (11) via the dimer [RhH2Cl(3)](2) (10) as an intermediate. In the presence of ethene, 11 is reconverted to 9. The reaction of 8 (olefin = C8H14) with the phosphonium salt 3(.)HCI affords a mixture of [RhHCl2(3)](2) (12) and 3, which upon warming at 60 degreesC produces [RhHCl2(3)(2)] (13). The attempted separation of 12 by column chromatography on Al2O3 led unexpectedly to the formation of the novel half-sandwich-type compound [(eta(6)-2,6-Me2C6H3CH2CH2PtBu2-kappaP)RhCl] (14). Treatment of either 8 or 14 with CO gives cis-[RhCl(CO)(2)(3)] (15), which represents the first structurally characterized dicarbonyl complex with the CO ligands in a cis disposition. In the absence of carbon monoxide, 15 is rather labile and readily converted to [RhCI(CO)(3)12 (16). The reaction of 9 with HCl affords the dinuclear ethylrhodium(III) compound 18, being built up by two 14-electron [RhCl2(C2H5)(3)] units. These units are linked by two bridging chlorides which are unsymmetrically situated between the two metal centers. Compound 18 reacts with CO to give 15 and with 3 to give 13, presumably in both cases via [RhHCl2(C2H4)(3)] as an intermediate. The half-sandwich-type complexes [(eta(6)-2,6-Me2C6H3CH2CH2PtBu2-kappaP)Rh(olefin)]PF6 (20, 21), obtained from [Rh(acetone)(2)(C8H14)(2)]PF6 as the precursor, react in acetone in the presence of H-2 to give [RhH2(acetone)(3)(3)]PF6 (22), which upon addition of diethyl ether generates the dihydride [(eta(6)-2,6-Me2C6H3CH2CH2PtBu2-kappaP)RhH2]PF6 (23). Compound 23 is a suitable starting material for the preparation of compounds having the general composition [(eta(6)-2,6-Me2C6H3CH2CH2PtBu2-kappaP)Rh(L)]PF6, where L is acetone, CH2=CHR (R = tBu, Ph), PhCequivalent toCH, and CO, respectively.