Three‐centre RhHSn bonds: an NMR study of the effects of varying the electron density on rhodium

The complexes [Rh(X)(H)(SnPh 3 )(PPh 3 )(L)] (X = NCBPh 3 (a), N(CN) 2 (b), NCS (c), NCO (d), N 3 (e); L = 1‐methylimidazole) ( 1 ) show systematic changes in δ ( 119 Sn), δ ( 103 Rh), J ( 119 Sn– 1 H) and J ( 119 Sn– 103 Rh) that are related to the electron‐donating properties of X. As X becomes more electron‐rich, δ ( 103 Rh), J ( 119 Sn– 1 H) and J ( 119 Sn– 103 Rh) increase and δ 119 Sn) decreases. The related complexes trans ‐[Rh(X)(H)(SnPh 3 )(PPh 3 ) 2 (L)] (X = N(CN) 2 , NCO; L = 4‐carboxymethylpyridine (x), pyridine (y) and 4‐dimethylaminopyridine (z)) ( 2 ), show a continuation of the trends in δ ( 119 Sn) and J ( 119 Sn– 1 H), but not δ ( 103 Rh) or J ( 119 Sn– 103 Rh). Data for 1 and 2 show that within certain limits of type of ligand varied (X = N‐donor, L = a pyridine) and coordination geometry, the response of δ ( 119 Sn) and J ( 119 Sn– 1 H) to changes in electron density on rhodium is largely independent of the means by which the change is effected.Copyright © 2001 John Wiley & Sons, Ltd.