Influence of Steric Factors on the Structures of Palladium Carbonyl Carboxylate Clusters: Synthesis and the Crystal Structure of the Hexanuclear Cluster Pd_6(mu-CO)_6[mu-OCOC(CH_3)_3]_6

摘要

New palladium(I) carbonyl carboxylate complexes of composition [Pd(CO)(OCOR)]_n, where R is a linear or branched alkyl fragment C_nH_(2n+1) (n = 3, 4, or 5), were synthesized. The presence of bulky alkyl fragments in the carboxylate ligand increases the nuclearity of the cluster compared to that of the starting palladium(I) carbonyl acetate of composition Pd_4(CO)_4(OAc)_4 (I) due, apparently, to steric hindrance. The replacement of acetate groups with pivalale groups [OCOCMe_3] affords the hexanuclear cluster Pd_6(CO)_6(OCOCMe_3)_6 (II). The structure of cluster II was established by X-ray diffraction analysis. The crystals of II (C_(42)H_(60)O_(18)Pd_6, M = 1491.30) belong to the orthorhombic system, space group P2_12_12_1, a = 10.758(2) k,b = 26.291 (5) A, c = 19.067(3) A, V = 5393(2) A~3, Z = 4. The cyclic metal core of cluster II is planar (within 0.12 A). Alternating pairs of pivalate and carbonyl ligands are coordinated on opposite sides of the metal core.