Reactions of Sn(NMe2)2 with Alkali-Metal tert-Butylphosphides tBuPHM (M = Li, Na, K): Evidence for Metal-Induced Modification of the Tin(II) Phosphinidene Anions

The 1:2 or 1:3 stoichiometric reactions of Sn(NMe 2 ) 2 with t BuPHM (M = Li, Na, K) in THF give the heterometallic alkali-metal/Sn(II) phosphinidene cages [{Sn 2 (PtBu) 3 } 2 Li 4 .4THF] (1), [{Sn 3 (P t Bu) 4 }Na.3THF] - -[Na(THF) 6 ] + (2), [{Sn 3 (P t Bu)4}2(K.THF) 3 ] - [K(THF) 6 ] + (4), and [{Sn 4 (P t Bu) 5 }K 2 .5THF] (5) (THF = C 4 H 8 O). The 2:3 → 3:4 → 4:5 numerical progression observed in the Sn(II):P t Bu ratios of the [{Sn 2 (P t Bu) 3 } 2 ] 4 - , {{Sn 3 (P t Bu) 4 }] 2 - , and [{Sn 4 (P t Bu) 5 }] 2 - anions of these complexes is dependent on the alkali-metal countercations present. The fact that the Lewis base donor has no effect on the resulting Sn(II) phosphinidene anions is indicated by the formation of the PMDETA-solvated complex [{Sn 3 (PtBu) 4 }Na 2 .2PMDETA.THF] (3) (PMDETA = (Me 2 NCH 2 CH 2 ) 2 NMe) in the 1:2 reaction of Sn(NMe 2 ) 2 with t BuPHNa in the presence of PMDETA (containing the same [{Sn 3 (P t Bu) 4 }] 2 - dianion as found in 2). The syntheses and X-ray structures of the new complexes 2-5 are discussed in relation to those of the previously reported complex 1.