DIPHOSPHINE-BRIDGED HETEROBIMETALLIC HYDRIDE AND CARBONYL-COMPLEXES OF RHODIUM AND IRIDIUM - STRUCTURE OF [RHIR(CO)3(PH2PCH2PPH2)2], A COMPLEX CONTAINING AN IR(-I)-]RH(I) DATIVE BOND

The reaction of [RhIrCl2(CO)2(dppm)2] (dppm = Ph2PCH2PPh2) with NaBH4under CO gives [RhIr(CO)3(dppm)2] (1), while under H2the product is [RhIr(H)(CO)2μ-H)(dppm)2] (2). The former is convertible to the latter via reaction with H2, while the reverse process proceeds under CO atmosphere. Addition of 1 equiv of HBF4-OEt2to 1 yields [RhIr(CO)3(μ-H)(dppm)2] [BF4] (3) and addition of a second equivalent leads to [RhIr(CO)3(μ-H)2(dppm)2] [BF4]2(4); both protonations are reversible. Protonation of 2 produces [RhIr(H)(CO)2(μ-H)2(dppm)2][BF4] (5). Like their neutral precursors, the protonated tricarbonyl and trihydride complexes may be interconverted via the appropriate hydrogenation or carbonylation processes. An X-ray structural determination of [RhIr(CO)3(dppm)3] shows it to have a non-A-frame structure, with one of the two carbonyls attached to Ir oriented toward Rh in what might be considered a weakly semibridging manner; furthermore, the phosphine groups on Ir have a cis arrangement with a P-Ir-P angle of 104.95 (7)°. The rhodium center is square planar as expected for a Rh(I) formulation, while the geometry about iridium is a distorted tetrahedron (if the Rh-lr bond is omitted) suggesting an Ir(-I) formulation. As such the Ir(CO)2P2-moiety can be considered as a pseudohalide, bound via a dative Ir-Rh bond. This compound crystallizes in the monoclinic space group P21/c with a = 20.296 (4) Å,b = 12.190 (7) Å, c = 19.064 (7) Å, 0 = 95.11 (2)°, and Z = 4. The structure was refined to R = 0.047 and Rw= 0.053 on the basis of 5208 unique observed reflections and 559 parameters varied. © 1990, American Chemical Society. All rights reserved.