Electronic Structure of N₂P₂ Four-Membered Rings and the Effect of Their Ligand Coordination to M(CO)₅ (Cr, Mo, and W)

Abstract

In this article the biradicaloid character of the ground-state structures of N2P2R2 (R = CH3) rings is studied using the DFT and CASSCF methods, and a satisfactory agreement of the B3LYP functional and CASSCF(6,6) ab initio method has been found. In order to obtain an adequate description of the biradicaloid character, we have combined two criteria: (i) singlet–triplet energy gaps and (ii) relative values of the occupation numbers for bonding and antibonding orbitals associated with the radical sites. We have analyzed how the biradicaloid character of the N2P2R2 ring changes upon coordination to M(CO)5 (M = Cr, Mo, and W) at the B3LYP/6-311+G* level of theory. Interestingly, in some cases the biradicaloid character increases dramatically upon complexation of the N2P2R2 ligands.

Biradicaloid and Zwitterion Reactivity of Dicarbondiphosphide Stabilized with N‐Heterocyclic Carbenes

“…Furthermore, a natural bond orbital (NBO) analysis confirmed that there is still one lone pair on each phosphorus atom, but the σ 3 ‐P I center (natural population analysis (NPA) charge: +0.398) is more electron rich than the noncoordinated phosphorus center (NPA charge: +0.487), which makes it plausible that in every case the second Lewis acidic moiety is coordinated to the same P atom as the first. Related gold complexes of biradicaloid III (Scheme ) have been reported recently by Schulz et al., and group 6 complexes have been studied computationally by Frontera and Streubel . Similarly, when 1 b was treated with two equivalents of Cu I Cl, ( IPr ) 2 C 2 PP(CuCl) 2 ( 9 ) was isolated as a dark red solid.…”

On the behaviour of biradicaloid [P(μ-NTer)]2towards Lewis acids and bases

“…3 To date, several examples of stable cyclic singlet biradicaloids have been known, which recently were parts of excellent reviews by F. Breher, M. Abe, and Rivard et al [4][5][6] The chemistry of singlet biradicaloids is rich and was investigated mainly in the examples of [ClC(m-PMes*)] 2 (Mes* = 2,4,6-tri(tertbutyl)phenyl) by the groups of Niecke [7][8][9][10] and Yoshifuji [11][12][13] and [ i Pr 2 P(m-B t Bu)] 2 by Bertrand et al [14][15][16] More recently, the activation of small molecules [17][18][19][20][21] and the one-electron oxidation 22 23 and several other small molecules like alkynes, alkenes, diazenes, azides, diazomethanes, isonitriles, nitriles, or nitrosotoluene. [24][25][26][27] It is noteworthy to mention that in a recent computational study by Streubel and Frontera et al, 28 several isomers of complexes of P 2 N 2 singlet biradicaloids were investigated, based on complexes which were experimentally obtained 29 by the group of Paine in the early 1980s as a result of the first attempt of the reduction of dichlorodiphosphadiazanes [ClP(m-NR)] 2 (R = e.g. t Bu).…”

Blocking Intramolecular Cycloadditions between C≡C Triple Bonds and Electrophilic Phosphinidene Complexes: Generation of Intermediates Able To React with Arenes

“…We were intrigued by this quite original reaction and decided to investigate some of its aspects by DFT calculations at the B3PW91/6-31+G­(d,p)-Lanl2dz (W) level . It must be stressed here that a theoretical study of a biradicaloid M­(CO) 5 complex has revealed a satisfactory agreement between the DFT and higher level CASSCF methods . The overall reaction combines a cyclization and a C–H insertion.…”

“…6 It must be stressed here that a theoretical study of a biradicaloid M(CO) 5 complex has revealed a satisfactory agreement between the DFT and higher level CASSCF methods. 7 The overall reaction combines a cyclization and a C−H insertion. Since most of the cycloadditions of electrophilic terminal phosphinidene complexes with alkynes are run in boiling toluene, it is well established that these phosphinidene complexes are unable to activate the C−H bonds of toluene.…”