A Comparative Assessment of the Effect of the Lewis Acidity of the Central Tin Atom on Intramolecular Coordination of (3‐Methoxypropyl)stannanes

The recently studied set of (3‐methoxypropyl)stannanes of general formula R x SnCl 4– x [R = (CH 2 ) 3 OCH 3 , x = 4 ( 1 ), x = 3 ( 2 ), x = 2 ( 3 ) and x = 1 ( 4 )] is extended with two new sets of (3‐methoxypropyl)stannanes of general formula RPh 3– x SnCl x [ x = 0 ( 5 ), x = 1 ( 6 ) and x = 2 ( 7 )] and RSn(S 2 CNEt 2 ) 3– x Cl x [ x = 0 ( 8 ), x = 1 ( 9 ) and x = 2 ( 10 )]. The molecular structures of 6 , 7 , 9 and 10 in the solid state were determined by X‐ray diffraction. In compounds 6 and 7 , the 3‐methoxypropyl ligand forms a C,O‐chelate and the tin atom is coordinated as a distorted trigonal bipyramid with the oxygen and one chlorine atom in the axial positions. Compounds 9 and 10 are hexacoordinate with a distorted octahedral ligand arrangement. While the 3‐methoxypropyl ligand in 10 also forms a C,O‐chelate, the oxygen atom in 9 is not coordinated to the central tin atom. The structures in a non‐coordinating (CDCl 3 ) and a coordinating solvent ([D 6 ]DMSO) were studied by multinuclear 1 H, 13 C and 119 Sn NMR spectroscopy. It is proposed that the structures found in the solid state are retained upon dissolution in CDCl 3 . Compounds 5 , 8 and 9 also preserve their structures in [D 6 ]DMSO. On the other hand, an equilibrium, in which one or more molecules of solvent enter the coordination sphere of the central tin atom and cleave the oxastannacycle, is established in [D 6 ]DMSO solutions of 6 , 7 and 10 . A comparison of the J     1 H,   119 Sncoupling constants obtained from 1D 1 H, 119 Sn HMQC and 2D 1 H, 119 Sn J‐HMBC spectra and the J     13 C,   119 Sncoupling constants derived from conventional 1D 13 C NMR spectra shows that the best indicator of the O→Sn donor–acceptor interaction in 3‐methoxypropylstannanes is the 3 J     13 C,   119 Snvalue. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)