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A study of the 1H and 119Sn NMR spectra of (CH3)4−nSn(NR2)n compounds (RCH3, C2H5)

1973; Elsevier BV; Volume: 61; Linguagem: Inglês

10.1016/s0022-328x(00)86547-x

1872-8561

E. Vanden Berghe, G.P. Van Der Kelen,

Organometallic Compounds Synthesis and Characterization

The 1H and 119Sn NMR spectra of the aminostannanes, (CH3)4−nSn(NR2)n (RCH3 and C2H5; n = 1−4) have been studied. The previously undetected 117,119SnNCH coupling in the methylaminostannanes was observed in these experiments thus making the proposal of a fast exchange of amine groups made by other authors difficult to sustain. From consideration of the 119Sn chemical shifts and the coupling constants 117,119SnCH, 117,119SnNCH, it has been shown that back-donation from the nitrogen lone pair to the vacant d orbitals of Sn is of little or no importance. On the other hand a significant intermolecular association via NH bridges apparently occurs in solutions of (CH3)3SnN(CH3)2 and (CH3)2Sn[Sn[N(CH3)2]2. It is suggested that weaker van der Waals interactions than these occur in other (CH3)4−nSnXn compounds which contain bulky X substituents and that these interactions explain the low 117,119SnCH coupling constants of the compounds studied. The percentage s character is both Sn→CH3 and Sn→NR2 orbitals increases with increasing NR2 substitution. The percentage s character increases in the SnCH3 orbitals in the order N(CH3)2>N(C2H5)2 while a corresponding decrease occurs in the Sn→NR2 orbitals with the same substitution sequence.