On the d6-Transition Metal Complex Formation of Electron-Rich Methylenephosphanes, a Quantum Chemical Investigation

Abstract

Keywords: Ab initio calculations / Density functional theory / Methylenephosphanes / Carbonyl complexes d 6 -Transition metal fragments M(CO) 5 (M = Cr, Mo, W) form mono-and binuclear complexes with methylenephosphanes. In the mononuclear complexes the metal fragment adds to the lone pair at the phosphorus atom without considerable geometrical change of the original phosphaalkene moiety. Amino substitution at the phosphorus atom yields a slightly more stable complex than amino substitution at the carbon atom. The latter substitution pattern causes an inverse polarization of the P−C π-bond. As a further consequence, in the corresponding transition metal complexes, the phosphorus

Metal carbonyl complexes of phosphaamidines. Coordinative integrity detected in C-amino(λ3,σ2)-phosphaalkene isomers coordinated through n(P) HOMO−1 donor orbitals

“…More recently, DFT calculations using modified SBK effective core potential basis sets were reported in which two model ligands, namely HPvCH 2 and HPvC(H)-NH 2 , are coordinated to M(CO) 5 (M = Cr, Mo, W). 51 This paper seems primarily devoted to explaining the highly-distorted coordination mode exhibited in 14 and 15, including the discovery that complex 14 is capable of attaching to a second Cr(CO) 5 group at P. 70 These studies demonstrate that such bis metal coordination is likely induced by the strongly electron-withdrawing CF 3 groups at P. The calculations also show that the geometry of the model phosphaalkene and aminophosphaalkene do not change much in the singly-coordinated, κP mode. This report is scarce in other details of the calculations and does not address the electronic structures of these complexes in detail.…”

“…49 The latter three types are sometimes referred to as 'polarized phosphaalkenes' or as having 'reverse electron demand' compared to R′PvCR 2 and R′PvCRR″. 50,51 Our entry into this field of research was from organic amidinates which can be tuned with a wide variety of substituents R, R′ and R″ in the R′NC(R)NR″ positions, and can be synthesised by many routes, of which the deprotonation of R′NC(R)-NHR″ is the most common and the most versatile. 52 Thus after preparing a series of amidines 7 using the bulky 2,6-diisopropylphenyl (Dipp) group for R′ and R″ with R = aryl, methyl or trifluoromethyl on the carbon backbone (see Scheme 1), [53][54][55] our aim is to prepare and investigate phosphaamidines that are exact molecular copies exchanging only N for P.…”

“…7c also shows the filled aromatic π orbitals from the Mes and Ph rings that are not present in the simple model ligands. 51 The interaction of these fragments to form 18 is dominated by σ-bonding between the metal LUMO (d z 2) and the HOMO−1 of the phosphaalkene. The bonding interaction stabilizes well below the filled aromatic π orbitals (shown as boxes in the diagram).…”

“…These differ from 17 by the presence of the strongly donating nitrogen p x orbital (not shown), resulting in a new π(1) that has strong CvN π bonding character. 51 As a consequence, the HOMO is now π(2) and is raised considerably in energy compared to the HOMO Finally, in (v) the in-phase d-p π interaction has more metal than ligand character in 10 than is the case for the equivalent orbital in 18. This difference in the characters of HOMO and HOMO−3 is a direct consequence of the higher-lying ligand π HOMO in 9 compared to 17.…”