CONDENSATION OF OS(CO)4(ETA(2)-HCCH) WITH CPRH(CO)(PR3) - UNEXPECTED PHOSPHINE DEPENDENCE IN THE FORMATION OF DIMETALLACYCLES - REVERSE REGIOCHEMISTRY AND A ZWITTERIONIC COMPOUND

The reaction of Os(CO)4(eta2-HCCH) with CpRh(CO)(PR3) (PR3 = PMe3, PMe 2Ph, PMePh2; Cp = C5H5) yields heterodimetallic compounds, but rather unexpectedly, two different types of complexes are obtained, dependent on the phosphine ligand. One compound class containing [mu-eta3:eta1- C(O)C2H2]Os(CO)3-RhCp(PMe2Ph) (3a) and its PMePh2 analogue (3b) is bas ed upon a dimetallacyclopentenone ring. The second structural type con tains [mu-eta1:eta2-HCCH(PMe3)](mu-CO)Os(CO)3RhCp (4) and can be descr ibed as a zwitterionic hydrocarbyl-bridged dimetallic species. The mol ecular structure of 4 has been confirmed by X-ray crystallography. Cry stals of 4 belong to the orthorhombic space group P2(1)2(1)2(1) with a = 8.093(2) angstrom, b = 16.116(3) angstrom, c = 12.959(2) angstrom, V = 1690(1) angstrom3, Z = 4, R = 0.050, and R(w) = 0.060.