[Ni(NHC)₂] as a Scaffold for Structurally Characterized trans [H−Ni−PR₂] and trans [R₂P−Ni−PR₂] Complexes

Abstract

The addition of PPh 2 H, PPhMeH, PPhH 2 , P(para-Tol)H 2 , PMesH 2 and PH 3 to the two-coordinate Ni 0 Nheterocyclic carbene species [Ni(NHC) 2 ] (NHC = IiPr 2 , IMe 4 , IEt 2 Me 2 ) affords a series of mononuclear, terminal phosphido nickel complexes. Structural characterisation of nine of these compounds shows that they have unusual trans [HÀ NiÀ PR 2 ] or novel trans [R 2 PÀ NiÀ PR 2 ] geometries. The bis-phosphido complexes are more accessible when smaller NHCs (IMe 4 > IEt 2 Me 2 > IiPr 2 ) and phosphines are employed. PÀ P activation of the diphosphines R 2 PÀ PR 2 (R 2 = Ph 2 , PhMe) provides an alternative route to some of the [Ni(NHC) 2 (PR 2 ) 2 ] complexes.DFT calculations capture these trends with PÀ H bond activation proceeding from unconventional phosphine adducts in which the H substituent bridges the NiÀ P bond. PÀ P bond activation from [Ni(NHC) 2 (Ph 2 PÀ PPh 2 )] adducts proceeds with computed barriers below 10 kcal mol À 1 . The ability of the [Ni(NHC) 2 ] moiety to afford isolable terminal phosphido products reflects the stability of the NiÀ NHC bond that prevents ligand dissociation and onward reaction.

Influence of the Flexibility of Nickel PCP‐Pincer Complexes on C−H and P−C Bond Activation and Ethylene Reactivity: A Combined Experimental and Theoretical Investigation

“…The 31 P NMR singlet of 8 at δ 4.0 is replaced in [Ni(PPh 2 )(CC NHC P)] ( 15 ) by an AB pattern at δ=48.32 and 16.68 ( 2 J (P−P)=30.1 Hz) for the phosphanido and phosphane ligands, respectively. The chemical shift of the former resonance is consistent with values reported very recently for Ni II complexes containing terminal diphenylphosphanido ligands [81] . The Ni1−C1 and Ni1−C16 bond lengths of 1.934(2) and 1.935(2) Å are consistent with C sp2 ‐hybridized carbon atoms.…”

“…The chemical shift of the former resonance is consistent with values reported very recently for Ni II complexes containing terminal diphenylphosphanido ligands. [81] The Ni1À C1 and Ni1À C16 bond lengths of 1.934(2) and 1.935(2) Å are consistent with C sp2 -hybridized carbon atoms. The Ni1À P2 bond length of 2.2178(5) Å indicates a terminal phosphanido ligand in trans position to a ligand with a strong trans-influence.…”

“…The Ni1−C1 and Ni1−C16 bond lengths of 1.934(2) and 1.935(2) Å are consistent with C sp2 ‐hybridized carbon atoms. The Ni1−P2 bond length of 2.2178(5) Å indicates a terminal phosphanido ligand in trans position to a ligand with a strong trans‐influence [81] . The Ni1−P1 bond length of 2.2019(5) Å is also indicative of the trans influence of the aryl ligand at C16.…”

“…The Ni1À P2 bond length of 2.2178(5) Å indicates a terminal phosphanido ligand in trans position to a ligand with a strong trans-influence. [81] The Ni1À P1 bond length of 2.2019(5) Å is also indicative of the trans influence of the aryl ligand at C16. It is interesting to recall that reactions related to a "reverse" of the PÀ C bond breaking reaction leading to 15 were observed (i) in Ni II phosphinite/phosphane complexes, [82] (ii) when metallacyclic Pd II complexes containing C,P and P,O chelates were reacted with PPhCl 2 with formation of CÀ P and OÀ P bonds, [83,84] and in Pt cluster chemistry with the reductive coupling of a bridging μ-PPh 2 group with a cis-phenyl ligand to form a PPh 3 ligand.…”

Isolation and Reactivity of Homoleptic Diphosphene Lead Complexes

“…[22] The P1À P2 and P3À P4 distances in 2 are 2.124(2) and 2.139(2) Å, which are shorter than those typically observed for a PÀ P single bond (2.20-2.25 Å) and lies in the average distances for a transitionmetal diphosphene π-complex (2.081-2.197 Å). [12,19,20] The long P•••P distances between the P 2 moieties (P1•••P3, 3.380 Å; P2•••P3, 3.461 Å) exclude any significant PÀ P bonding between two P 2 units. These bond lengths imply that the interaction between the Pb atom and the P 2 moieties are considered as π-bonding rather than σ-bonding.…”