Carbodiphosphorane-based nickel pincer complexes and their (de)protonated analogues: dimerisation, ligand tautomers and proton affinities

Abstract

The reactivity patterns of carbodiphosphoranes (CDPs) as ligands are much less explored than those of isoelectronic analogues. In the current manuscript, we investigate the reactivity of the carbodiphosphorane-based PCP nickel(ii) pincer complex [({dppm}2C)NiCl]Cl (1) towards acids and bases, calculate proton affinities, analyse the bonding situation and tautomeric forms with the aim to evaluate whether CDPs can potentially act as cooperative ligands in catalysis (dppm = 1,1-bis(diphenylphosphino)methane). Our investigations show that different tautomeric forms are stable for the coordinated and the uncoordinated ligand. The protonated CDP-based complex 2 represents a rare example of a cationic donor group binding to a cationic metal centre. The continuous arm-deprotonation of 1 leads to the formation of remarkably stable dimers with Ni-C-P-C-metallacycles. In comparison to corresponding boron and amine-based ligands, the coordinated CDP-group exhibits the lowest proton affinity according to DFT calculations, indicating that coordinated CDP ligands can potentially serve as proton relay in cooperative catalysis.

Ligands Based on Phosphine‐Stabilized Aluminum(I), Boron(I), and Carbon(0)

“…The partial charge at the boron atom of the phosphine-stabilized borylene in 1a Me is calculated to be À0.65 e, but the positive partial charge at aluminumi n1b Me (+ 1.01 e) already indicates that the bonding situation is different in the heavier homologue.Acloser look at the hydrogen atoms reveals decisive differences in the polarity of the EÀHb ond:t he positivep artial chargeo f+ 0.25 e at the hydrogen atom, which is boundt ot he negatively charged carbon atom in 1c Me ,isinline with the experimentally observed facile deprotonation of donor groups based on (R 3 P) 2 CH + . [14] In comparison, the boron-hydrogen bond in 1a Me is significantly less polar, with ap artial charge close to zerof or the hydrogen atom (+ 0.04 e). The negative partial charge of À0.40 e in 1b Me ,i n combination with the positively charged aluminuma tom, suggests ah ydridic nature of this donor group.…”

Cu(I) Complexes of Multidentate N,C,N- and P,C,P-Carbodiphosphorane Ligands and Their Photoluminescence

“…Peringer et al developed P , C , P –CDP pincer complexes of a formal carbone ligand C(dppm) 2 , which was not isolated and characterized, but trapped in the form of its complexes [ 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. The synthetic strategy involved complex redox reactions.…”

“…A topic of current interest is introducing secondary ligand functions into the CDP frame: Cyclometalation with noble metals rhodium and platinum gave rise to the characterization of C , C , C -pincer ligand complexes with two cyclometalated phenyl rings [ 12 , 13 , 14 , 15 , 16 , 17 ], and an ortho-directed double lithiation of hexaphenyl-carbodiphosphorane leads to lithium complexes that are capable of transfering the C,C,C -pincer ligand synthon [CDP] 2− to any other element of the periodic table [ 17 ]. P , C , P -chelate complexes of a phosphine functionalized CDP ligand CDP(CH 2 PPh 2 ) 2 ( 13 ), formally a carbone C(dppm) 2 (dppm = bis-diphenylphosphinomethane), were characterized, but the free ligand 13 was not isolated so far [ 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. Only recently, complexes of 2-pyridyl functionalized N , C , N -carbodiphosphorane CDP(Py) 2 ( 1 ) have been reported [ 25 , 26 ].…”

Cu(I) Complexes of Multidentate N,C,N- and P,C,P-Carbodiphosphorane Ligands and their Photoluminescence

“…Peringer et al developed P,C,P-CDP pincer complexes of a formal carbone ligand C(dppm)2, which was not isolated and characterized, but trapped in form of its complexes [18][19][20][21][22][23][24]. The synthetic strategy involved complex redox reactions.…”

“…A topic of current interest is introducing secondary ligand functions into the CDP frame: Cyclometalation with noble metals rhodium and platinum gave rise to the characterization of C,C,C-pincer ligand complexes with two cyclometalated phenyl rings [12][13][14][15][16][17], and ortho-directed double lithiation of hexaphenyl-carbodiphosphorane leads to lithium complexes capable to transfer the C,C,C-pincer ligand synthon [CDP] 2-to any other element of the periodic table [17]. P,C,P-chelate complexes of a phosphine functionalized CDP ligand CDP(CH2PPh2)2 (13), formally a carbone C(dppm)2 (dppm = bis-diphenylphosphinomethane), were characterized, but the free ligand 13 was not isolated so far [18][19][20][21][22][23][24]. Only recently, complexes of 2pyridyl functionalized N,C,N-carbodiphosphorane CDP(Py)2 (1) were reported [25,26].…”