Borole derivatives: X. Syntheses of (η 5-borole)metal complexes via borole ammonia adducts. Complexes of the chromium group metals and the crystal and molecular structures of tetracarbonyl [η 5-(1-phenylborole)] chromium and its molybdenum analogue

Abstract

The 1 H-Borole ammonia adducts C 4H 4BR · NH 3 (R = Me, Ph) (Ia,b) have been made by ammonia degradation of the (η 5-borole)carbonyliodocobalt complexes (C 4H 4BR)Co(CO) 2I (VIa,b). They are the simplest 1 H-borole derivatives obtained to date, and have been identified in solution by NMR spectroscopy. Reactions starting from Ia,b have given otherwise inaccessible (η 5-borole)metal complexes such as (η 5-C 4H 4BMe)Cr(CO) 4 (II) and (η 5-C 4H 4BPh)M(CO) 4 (III: M = Cr, IV: M = Mo, V: M = W). X-ray diffraction studies on III and IV show them to have distorted piano stool structures with bond lengths CrB,240.3(2) and MoB 253.4(4) pm. Site exchange processes within the M(CO) 4 groups are fast on the 13C NMR time scale even at 155 K.