Synthesis and Structural Characterization of Two Tetraruthenium Bis(phosphinidene) Clusters with 62- and 64-Electron Counts: Ru4(CO)11(μ4-PPh)(μ4-PNPri2) and Ru4(CO)12(μ4-PNPri2)2

The clusters Ru 4 (CO) 10 (μ-CO)(μ 4 -PPh)(μ 4 -PNPr i 2 ) ( 6 ) and Ru 4 (CO) 12 (μ 4 -PNPr i 2 ) 2 ( 7 ) have been prepared via the reactions of Cl 2 PNPr i 2 with, respectively, [Ru 4 (CO) 12 )(μ 3 -PPh)] 2 - ( 5 ) and [Ru 4 (CO) 12 ] 4 - . The dianion 5 has been generated from the reduction of [Ru 4 (CO) 13 )(μ 3 -PPh)] ( 2 ) by CoCp 2 . The structures of 5 [CoCp 2 ] 2, 6, and 7 were determined by X-ray crystallography. The structure of the dianion 5 resembles that of its precursor [Ru 4 (CO) 13 )(μ 3 -PPh)] ( 2 ) and consists of a square pyramidal framework of four Ru(CO) 3 fragments with a PPh group occupying a basal position. Thus, loss of a CO ligand via two electron reduction leads to relatively small structural changes. There are 10 terminal carbonyls and 1 bridging carbonyl in 6, and the four Ru atoms have a square planar arrangement with the two different phosphinidene ligands each capping one side of the Ru 4 square. There are, however, 12 terminal carbonyls in 7, and the Ru 4 arrangement is a significantly puckered square (dihedral angle 135.4 °C). Each phosphinidene ligand in 7 caps one side of the Ru 4 framework and has two very long and two normal Ru−P distances. The P−P distance in 7 is 3.152 Å, the longest value reported to date for this type of M 4 P 2 compound.