Phosphanylborohydrides: First Assessment of the Relative Lewis Basicities of [BH 3 PPh 2 ] – , CH 3 PPh 2 , and HPPh 2

The compounds K[PPh 2 ], HPPh 2 , CH 3 PPh 2 , BH 3 (H)PPh 2 , BBr 3 (H)PPh 2 , BH 3 (CH 3 )PPh 2 , BBr 3 (CH 3 )PPh 2 , [H 2 PPh 2 ]I, [CH 3 (H)PPh 2 ]I, [(CH 3 ) 2 PPh 2 ]I, and K[(BH 3 ) 2 PPh 2 ] have been investigated by NMR spectroscopy. In addition, X‐ray crystal structures have been determined for K(18‐crown‐6)[PPh 2 ], BBr 3 (H)PPh 2 , BBr 3 (CH 3 )PPh 2 , [H 2 PPh 2 ]I, [CH 3 (H)PPh 2 ]I, [(CH 3 ) 2 PPh 2 ]I, and K(18‐crown‐6)[(BH 3 ) 2 PPh 2 ]. An evaluation of coupling constants (e.g. 1 J PC i ; C i = ipso carbon atom of a phenyl ring) augmented by an inspection of key structural parameters (e.g. the angles C i –P–C i ′) leads to the conclusion that dative bonds originating from ligand [BH 3 PPh 2 ] – possess a significantly higher p character than dative bonds involving the ligands HPPh 2 and CH 3 PPh 2 . The 1 J PB values obtained for BH 3 (H)PPh 2 , BH 3 (CH 3 )PPh 2 , and [(BH 3 ) 2 PPh 2 ] – suggest [BH 3 PPh 2 ] – to form the strongest [BH 3 ] adduct of all three compounds which is in agreement with the results of displacement reactions employing the couples CH 3 PPh 2 /[(BH 3 ) 2 PPh 2 ] – and [BH 3 PPh 2 ] – /BH 3 (CH 3 )PPh 2 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)