Reactions of lithium dialkyl/phenyl phosphanylmethylides, RR′PCH(X)Li (R, R′ = Me, Et, Ph and R = Me, R′ = Ph; X = H or Me), with sulfur diimides S(NR′′)2 (R′′ = tBu or SiMe3) in an equimolar ratio yielded Janus head complexes with the structural motif [Li{RR′PCH(X)S(NR′′)2}]2 (R′′ = tBu, SiMe3). The basic core of these dimeric complexes is composed of a (LiN)2 four-membered ring containing two four-coordinated lithium atoms. A lithium complex of the new Janus head ligand with another structural motif [TMEDA·Li{Ph2PCH2S(NSiMe3)2}] (6) could be isolated from the reaction of [Ph2PCH2Li·TMEDA] with S(NSiMe3)2. Two monomeric complexes [Mg{Me2PCH2S(NR′′)2}2] (7, 8) were synthesised by a straightforward reaction of [Li{Me2PCH2S(NR′′)2}2] with MgCl2 in pentane. The magnesium atom is chelated by one phosphorus atom and two nitrogen atoms of each unit of the hemilabile ligand in a tripodal manner, leading to octahedral geometry around the magnesium cation. A complete analysis of [Ph2PCH2(SNSiMe3)(HNSiMe3)] (9) is also described in which one nitrogen atom of the imido moiety is protonated.
