A trigonal and hindered tertiary phosphine ligand rendered anionic by a niobate anchor : Formation of zwitterionic M ( I ) ( M 1⁄4 Cu , Ag , Au , Rh ) complexes †

Treatment of terminal phosphide anion [PNb(N[Np]Ar)3] ([Na(OEt2)] + salt, Ar 1⁄4 3,5-Me2C6H3) with two diphenylketene equivalents led to isolation of anion [P(C{CPh2}O)2Nb(N[Np]Ar)3] in 78% yield as its [Na(THF)] salt. The latter reacts with diphenylketene (1 equiv) to provide the triple diphenylketene addition product [P(C{CPh2}O)3Nb(N[Np]Ar)3] in 88% yield as its [Na(THF)] salt; the same material is obtained alternatively in 93% yield by reaction of diphenylketene (3 equiv) directly with niobium phosphide [Na(OEt2)][PNb(N[Np]Ar)3]. The anion [P(C{CPh2}O)3Nb(N[Np]Ar)3] was also crystallized as its ion-separated [Na(THF)6] + salt as illuminated by a single-crystal X-ray diffraction study, which also revealed the three-fold symmetric nature of the highly hindered tertiary phosphine comprising the anionic component. Coinage metal monocations of the new, anionic phosphine were prepared via salt elimination; structural studies on the zwitterionic complexes (py)M[P (C{CPh2}O)3Nb(N[Np]Ar)3] (M1⁄4Cu, Ag, and Au) showed them to be isostructural in the space group P21/c while illustrating the ensconcement of a two-coordinate coinage metal in a deep binding pocket flanked by three phenyl residues. Rhodium(I) incorporation into the anion’s binding pocket illustrated versatility of the latter: in contrast to structural observations for the M(I) complexes (M 1⁄4 Cu, Ag, and Au), in the case of Rh[P(C{CPh2}O)3Nb(N[Np]Ar)3] an X-ray study reveals strong interactions (h 6 and h, respectively) with two of the three phenyl residues that are proximal to Rh(I) when connected to the phosphine lone pair of the anion.