η1-Coordination of Phosphinine to Chromium, Molybdenum, and Tungsten † ,1

The homoleptic complexes hexakis(η1-phosphinine)molybdenum 10 and hexakis(η1-phosphinine)tungsten 11 have been prepared via reduction of suitable metal halides with magnesium or zinc in order to explore trends in the triad (η1-C5H5E)6M, 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 Å, 2) < Mo−P (2.38 Å, 10) ≈ W−P (2.37 Å, 11). The NMR data exhibit the same trends upon the η1-coordination of phosphinine as hexakis(η1-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.