Nickel nitrosyl complexes with diphosphines. The crystal and molecular structure of [(dppe)(ON)Ni(µ-dppe)Ni(NO)(dppe)][BF4]2(dppe = Ph2PCH2CH2PPh2)

Abstract

The preparation and characterization of several nitrosyl complexes of nickel with ditertiary phosphines (L–L) are reported. With the ligand Ph₂PCH₂PPh₂(dppm) the mononuclear complex [Ni(NO)(dppm)₂]BPh₄ is obtained, in which one diphosphine acts as unidentate and one as a chelating ligand. With R₂P(CH₂)_nPR₂(R = Ph or Me, n= 2 or 3) binuclear compounds [Ni₂(NO)₂(L–L)₃]Y₂(Y = BF₄ or BPh₄) are formed, in which one diphosphine bridges two Ni(NO)(L–L) moieties. I.r., u.v.–visible, and ³¹P n.m.r. data suggest a pseudo-tetrahedral co-ordination for the nickel atom with linear Ni–NO groups for both mono- and bi-nuclear species. Binuclear complexes containing phenyl-substituted diphosphines show an unusual low-temperature ³¹P n.m.r. behaviour which is interpreted in terms of slow Ni–P bond rotation. A series of complexes [Ni(NO)L(L–L)]Y [L = PHR₂, PR₃, or P(OR)₃; Y = BPh₄ or BF₄] has been prepared, and their low-temperature ³¹P n.m.r. behaviour compared with that of the binuclear species. The structure of [Ni₂(NO)₂(dppe)₃][BF₄]₂(dppe = Ph₂PCH₂CH₂PPh₂) has been determined by X-ray methods. Crystals are monoclinic, space group C2/c with Z= 4 in a unit cell of dimensions a= 35.073(8), b= 14.012(4), c= 17.351 (5)Å, and β= 112.24(2)°. The structure has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.0878 for 2 029 observed reflections. In the cation one dppe ligand acts as a bridge between the two nickel atoms, while the other two chelate the two metals. One nitrogen atom from a terminal nitrosyl ligand completes the distorted tetrahedral co-ordination around each Ni atom. The Ni–N bond distance and the Ni–N–O bond angle are 1.67(2)Å and 168.2(14)°, respectively.