Activation of white phosphorus in the coordination sphere of nickel complexes with σ-donor ligands

Abstract

Routes of white phosphorus activation in the coordination sphere of the nickel complexes with different ligands are shown. The first route is based on the coordination of a P 4 molecule with the metal, resulting in the deformation of the P 4 tetrahedron without destruction. This case is characteristic of the NiX 2 L complexes, which are reduced at higher cathodic potentials (|E red | > 0.9 V) (X = BF 4 , Br, and Cl; L is bpy in DMF, MeCN, and acetone; 2,9 dimethyl 1,10 phenanthroline (phen) and PPh 3 in DMF and acetone). To cleave the P-P bonds in the P 4 molecule, this complex should be reduced on the electrode. The second route is the oxidation of white phosphorus in the coordination sphere of the Ni II complex. It occurs when the complex has a sufficiently high oxidizing ability and is reduced rather easily (|E red | < 0.9 V) (X = BF 4 , L is 1,1,1 tris(diphenylphosphinomethyl)ethane (triphos) in acetone; 1,1´,5,5´ bis[methylenedi(p phenylene)]di(3,7 diphenyl 1,5 diaza 3,7 diphosphacyclooctane) (n 2 p 2 ) in DMF; phen and PPh 3 in MeCN). The P 4 molecule opening is observed to form a new Ni I complex containing the (P 3 ) fragment, for example, [(triphos)Ni(P 3 )Ni(triphos)](BF 4 ) 2 .The electrochemical activation of reagents in processes involving organometallic compounds is very efficient. 1-4 This approach combines advantages of catalysis by metal complexes and activation by means of electrochemical electron transfer. The activation of white phosphorus is a practically important task because of the necessity to search for new routes of direct syntheses of organophos phorus compounds. Numerous reactions of P 4 tetrahedron transformation were described, which resulted in various polyphosphorus structures among which metal complexes with cyclic P 3 , P 5 , and P 6 ligands, 4 as well as the P 4 ligand, 5,6 seem to be most interesting. The P 4 molecule is activated due to the deformation of the P 4 tetrahedron and, as a consequence, the P-P bond length changes. In ultimate cases, these bonds can cleave to form new polyphosphorus structures. Until now, P 4 transformation was studied only by NMR spectroscopy, and very stable compounds were examined. Evidently, the more stable these structures, the more difficult is the preparation of related basis organophosphorus compounds, i.e., the main task of the elemental phosphorus chemistry is the direct transformation of phosphorus into organophosphorus compounds (OPC), excluding traditional steps of its chlo rination. At the same time, metal complexes with poly phosphorus ligands can possess a set of useful properties: semiconductivity, corrosion resistance, and others 7 and act as stable intermediates in various reactions, which are of independent interest.In this work, we attempted to estimate the reactivity of several nickel complexes with σ donor ligands toward white phosphorus using cyclic voltammetry (CV), pre parative electrolysis, and 31 P NMR spectroscopy. The nickel complexes were chosen, because they are catalysts of some reactions of white phosphorus functio...

P4 Activation by Late-Transition Metal Complexes

“…For example, the complex [{(triphos)Ni} 2 (μ,η 3:3 - cyclo- P 3 )](BF 4 ) 2 ( 150 ) mentioned above could be obtained electrochemically via a one-pot reaction from Ni(BF 4 ) 2 , white phosphorus, and triphos. The functionalized P n R m fragment can itself be a ligand for Ni …”

Evaluation of Transition Metal Catalysts in Electrochemically Induced Aromatic Phosphonation

“…The complexes were synthesized by a known method [34,39,40]. The spectroscopic data for CoCl 2 bpy [55], Ni(BF 4 ) 2 bpy [56], and MnCl 2 bpy [56] complexes matched that reported in the literature.…”

Electrochemical Transformation of White Phosphorus as a Way to Compounds With Phosphorus-Hydrogen and Phosphorus-Carbon Bonds

“…The electrochemical reduction of white phosphorus was not studied in details up to now, the mechanism of its activation and transformation with P-P bond cleavage under electron transfer on electrodes of the various nature was not clear. The data on potentials of Р 4 reduction on glassy carbon and mercury were published earlier [23], the ways of transformation of white phosphorus under the complexes of nickel, including generated electrochemically were described [29][30][31].…”

“…Voltammetric (coulometric) studies of white phosphorus reduction were performed at mercury electrode in alcohol medium [49] and have shown the process to proceed at substantial negative potentials, the calculation of a number of electrons through the peak height giving the value of n close to unity in the concentration range from 0.05 to 1.6 mM, what practically coincides with white phosphorus solubility limit in these media. At glass carbonic electrode in aprotic media (DMFA, CH 3 CN) with modest addition of benzene the process proceeds at -2.20 V (Ag/AgNO 3 ), at concentration 5 mM a number of electrons being even slightly smaller than unity-0.7 with benzophenone standard [30]. At lead electrode white phosphorus reduces at similar values of potential (-2.20 V vs. Ag/AgNO 3 ; -1.86 V vs. SCE) and current.…”

“…The electrocatalytic functionalization of white phosphorus has been also accomplished using transition metal complexes as catalysts [52][53][54][55].The activation of P 4 takes place under mild conditions promoted by the electrogeneration of a carbanion in the presence of P 4 [30,[53][54][55]. The reaction has been documented for Ni(0) species stabilised by 2.2'-bpyridine (bpy) electrogenerated from Ni(II) complexes.…”