Synthesis and transformations of 60-, 62-, and 64-electron Co4(CO)x(PNR2)2 (x = 8, 9, 10) clusters

Abstract

A unique family of bis-(amino)phosphinidene Co4 clusters with electron counts in the 60–64 e regime is described. The 62-electron (5 Co–Co) butterfly compound [Co4(CO)8(µ-CO){µ3-P(TMP)}2] (TMP = 2,2,6,6-tetramethyl piperidyl) (1a) is obtained via condensation of the bridged (amino)phosphinidene complex [Co2(CO)6{µ-P(TMP)}]. Further heating and removal of CO gives the 60-electron (6 Co–Co) tetrahedral compound [Co4(CO)6(µ-CO)2{µ3-P(TMP)}2] (3a). The reaction of K[Co(CO)4] with PCl2(N-i-Pr2) gives the 64-electron (4 Co–Co) square-planar derivative [Co4(CO)8(µ-CO)2(µ4-PN-i-Pr2)2] (2), which loses one carbonyl ligand to form the 62-electron (5 Co–Co) butterfly compound [Co4(CO)8(µ-CO)(µ3-PN-i-Pr2)2] (1b). Complex 1b releases another carbonyl to form the 60-electron (6 Co–Co) tetrahedral compound [Co4(CO)6(µ-CO)2(µ3-PN-i-Pr2)2] (3b). X-ray structural analyses of compounds 1a, 1b, 2, and 3a have been carried out. The reversibility of the CO elimination reactions and the structural rearrangements accompanying changes in electron count in this series are discussed.Key words: cobalt, cluster compounds, phosphinidene, skeletal rearrangement.