Abstract
The IR and NMR spectra of the complexes [M(CO)6]Cl · HCl (M = Mn: 1, M = Re: 2), M(C0)5C02Et (M = Mn: 3, M = Re: 4), [Mn(CO)5PR3][PF6] (5; PR3 = PPh(OPh)2: a, P(n-Pr)3: b, PHPh2: c, PPh(NEt2)2: d, P(p-C6H4F)3: e), [Re(CO)5PHPh2][PF6] (6 c), Mn2(CO)8(PR3)2 (7) and Re2(CO)8(PHPh2)2 (8c) are discussed in the context of σ-and π-interactions in the metal-ligand system and compared with 51V NMR data of the analogous isoelectronic and isostructural carbonylvanadates (-I). On the basis of these results, the phosphines are arranged in the order of decreasing integral ligand strength according to a>b>c>d. The 55Mn shielding of 5 is greater than that of 1, which is explained by strong σ-interactions and correspondingly large e-a1* splitting dominating the paramagnetic deshielding term in the pseudooctahedral complexes of type 5. The only rhenium compound accessible to NMR is 2, for which the 185 Re and 187 Re resonances were obtained. 31P coordination shifts are positive for all complexes. Spectroscopic data for 7c show that this complex presumably has the structure (CO)5Mn-Mn(CO)3(PHPh2)2, contrasting 7a, 7b, 7d and 7e (local D4d symmetry).
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