Spectroscopic properties of compounds with Group 4B–transition-metal bonds. Part 2. Pentacarbonylrhenium and tetracarbonylcobalt complexes

Abstract

Established synthetic routes have been used to obtain the new complexes [Re(CO)₅(MMe₃)][M = Si(1) or Ge(2)]. Infrared and Raman spectra for (1), (2), and [Re(CO)₅(SnMe₃)](3) have been recorded and assigned, with ν(M–Re) at 297 (1), 175 (2), and 151 cm^–1(3). Mass-spectral fragmentation data are consistent with (i) increased metal–metal bond strength and (ii) increased transition-metal–carbonyl-carbon bond strength in (1)–(3) as compared with the manganese analogues. Appearance-potential measurements for ions [MMe₃]⁺ provide bond-dissociation energies D(M¹–M²) for (1)–(3) and for [Co(CO)₄(MMe₃)][M = Si (4), Ge (5), or Sn (6)] as follows: (1), 3.1; (2), 3.2 (3), 3.7; (4), >2.4; (5), 3.2; (6), 2.8 eV; that for complex (3) well exceeds any related datum and its significance is discussed.