h¹-Coordination of Phosphinine to Chromium, Molybdenum, and Tungsten

The homoleptic complexes hexakis(eta(1)-phosphinine)molybdenum 10 and hexakis(eta(1)-phosphinine)tungsten 11 have been prepared via reduction of suitable metal halides with magnesium or zinc in order to explore trends in the triad (eta(1)-C5H5E)(6)M, M = Cr, Mo, W. According to X-ray crystal structure determinations, 10 and 11 are isostructural and show almost ideal octahedral geometry of the metal-phosphorus core. The bond distances d(M-P) are relatively short in comparison to other homoleptic phosphane complexes of Mo and W; they follow the expected order: Cr-P (2.26 Angstrom, 2) < Mo-P (2.38 Angstrom, 10) approximate to W-P (2.37 Angstrom, 11). The NMR data exhibit the same trends upon the eta(1)-coordination of phosphinine as hexakis(eta(1)-phosphinine)chromium 2, but the change of the central metal from Cr to W results in an increased shielding of the neighboring atoms (P, ortho-H, and C) of the ligands. The UV-vis spectra of 10 and 11 in comparison to 2 display a continuous hypsochromic shift in the MLCT region. Conversely, the redox potentials for the couples ML6(+/0), which are increasingly anodic following the sequence Cr < W < Mo, show a discontinuous gradation.