Thiocyanogen Insertion into P−C Bonds of Diphosphinomethanide Complexes, Leading to Rare Functionalized Diphosphine and Tetraphosphine Ligands

Abstract

The complex fac-[Mn(CNtBu)(CO)3{(PPh2)2C−SCN}] (2) reacts with thiocyanogen, affording the unstable derivative fac-[Mn(CNtBu)(CO)3{(PPh2)C(SCN)C(SSCN)N(PPh2)}] (3), as a result of the insertion of the pseudohalogen molecule into one of the P−C bonds of the diphosphinomethanide ligand. This complex undergoes intermolecular sulfur−sulfur coupling processes, with elimination of the pseudohalogen molecules (SCN)2, S(CN)2, and (CN)2, to yield a mixture of the dinuclear complexes fac-[{Mn(CNtBu)(CO)3(PPh2)C(SCN)C(NPPh2)}2−Sn] (4−6) linked through polysulfide chains of different lengths. Treatment of these dinuclear disulfide and trisulfide derivatives with 1 or 2 equiv of HBF4 resulted in the sequential protonation of the nitrogen atoms of the ligand, yielding cationic and dicationic complexes, respectively. In the case of monoprotonated disulfide derivatives 31P NMR experiments reveal the existence of an intramolecular proton-transfer process between the endocyclic nitrogen atoms of both metallic fragments. Similar insertion reactions are observed in the treatment of other diphosphinomethanide complexes containing a P2C−S skeleton such as fac-[Mn(L)(CO)3{(PPh2)2C−SC(S)NMe2}] (11a, L = CNtBu; 11b, L = CO) and fac-[Mn(CNtBu)(CO)3{(PPh2)2C−S(C5NH3NO2)}] (12) with thiocyanogen, yielding new mononuclear derivatives, whose formation implies additionally unusual transposition and cyclization processes. These mononuclear complexes can be protonated on the nitrogen atom by addition of HBF4, affording complexes containing rare functionalized diphosphine ligands.