Synthesis, characterisation and reactivity of group 2 complexes with a thiopyridyl scorpionate ligand.

Herein we report the reactivity of the proligand tris(2-pyridylthio)methane (HTptm) with various Alkaline Earth (AE) reagents: (1) dialkylmagnesium reagents and (2) AE bis-amides (AE = Mg-Ba). Heteroleptic complexes of general formulae [Mg(Tptm)(R)] (R = Me, n Bu; Tptm = {C(S-C 5 H 4 N) 3 } - ) and [AE(Tptm)(N'')] (AE = Mg-Ba; N'' = {N(SiMe 3 ) 2 } - ) were targeted from the reaction of HTptm with R 2 Mg or [AE(N'') 2 ] 2 . Reaction of the proligand with dialkylmagnesium reagents led to formation of [{Mg(κ 3 C , N , N -C{Bu}{S-C 5 H 4 N} 2 )(μ-S-C 5 H 4 N)} 2 ] (1) and [{Mg(κ 3 C , N , N -C{Me}{S-C 5 H 4 N} 2 )(μ-OSiMe 3 )} 2 ] (2) respectively, as a result of a novel transfer of an alkyl group onto the methanide carbon with concomitant C-S bond cleavage. However, reactivity of bis-amide precursors for Mg and Ca did afford the target species [AE(Tptm)(N'')] (3-AE; AE = Mg-Ca), although these proved susceptible to ligand degradation processes. DFT calculations show that alkyl transfer in the putative [Mg(Tptm)( n Bu)] (1m') system and amide transfer in 3-Ca is a facile process that induces C-S bond cleavage in the Tptm ligand. 3-Mg and 3-Ca were also tested as catalysts for the hydrophosphination of selected alkenes and alkynes, including the first example of mono-hydrophosphination of 4-ethynylpyridine which was achieved with high conversions and excellent regio- and stereochemical control.