Preparation, crystal structures and spectroscopic properties of a series of cobalt(III) phosphine complexes: trans- and cis-[Co(dtc)_2(PMe_(3-n)Ph_n)_2]~+ (dtc = N,N-dimethyldithiocarbamate; n = 0, 1, 2 or 3)

摘要

A series of new cobalt(III) phosphine complexes of trans-[Co(dtc)_2(PMe_(3-n)Ph_n)_2]BF_4 (dtc - N,N-dimethyldithiocarbamate; n = 0, 1, 2 or 3) and cis-[Co(dtc)_2(PMe_3 or PMe_2Ph)_2](BF_4 or PF_6) have been prepared and their crystal structures and spectroscopic properties have been investigated. It is found that the Co-S bond lengths vary with steric and electronic factors of the P-ligands; i.e. (1) the intramolecular #pi#-#pi# stacking interaction between the dtc plane and the phenyl ring of the P-ligand,and (2) the electronic trans influence of the trans-positioned P-ligand. The strength of electronic trans influence decreases as PMe_3 > PMe_2Ph > P(OH_2) _3CEt in accordance with the order of #sigma#-donicity strengths. In the series of trans-isomers, the electronic trans influence is competitive with the steric requirement of the phosphine to elongate the mutually trans Co-P bonds. The steric trans influence via the equatorial dtc ligands for such an elongation of the Co-P bonds seems to be negligible, which is in sharp contrast to the situation for via pentane-2,4-dionate (acac) ligands in the analogous complexes, trans-[Co(acac)_2(PMe_(3-n)Ph_n)_2]PF_6. This is probable due to the compactness of dtc and the resulting open space at the Co atom. The fact that the Co-P bond lengths in the dtc complexes are shorter than those in the acac complexes is reflected in the larger stability toward hydrolysis of the dtc complexes. In the UV-vis absorption spectra, the degenerate splitting component (a~1E_g) of the first d-d transition band of trans-[Co(dtc)_2(PMe_(3-n)Ph_n)_2]~+ is observed at almost the same position (within 300 cm~(-1)) as that of the corresponding acac complexes, while the transition energies of the P-to-Co LMCT of these two series of complexes are rather different (at least 2700 cm~(-1)) from each other. Furthermore, the first and the second d-d transition bands of cis-[Co(dtc)_2(PMe_(3-n)Ph_n)_2]~+ are observed at lower energy than those of cis-[Co(dtc)_2{P(OMe_3}_2]~+ in spite of a weaker #sigma#-donor of phosphite. The separation of the first and the second d-d transition bands of the P(OMe)_3 complex is remarkably smaller than the separation of the bands of the PMe_3 one,being inducative of a further reduction of the interelectronic repulsion in the P(OMe)_3 complex.