Generating and Dimerizing the Transient 16‐Electron Phosphinidene Complex [Cp*IrPAr]: A Theoretical and Experimental Study

Abstract

The properties of the 16‐electron phosphinidene complex [CpRIrPR] were investigated experimentally and theoretically. Density functional theory calculations show a preferred bent geometry for the model complex [CpIrPH], in contrast to the linear structure of [CpIrNH]. Dimerization to give [{CpIrPH}2] and ligand addition to afford [Cp(L)IrPH] (L=PH3, CO) were calculated to give compounds that were energetically highly favorable, but which differed from the related imido complexes. Transient 16‐electron phosphinidene complex [Cp*IrPAr] could not be detected experimentally. Dehydrohalogenation of [Cp*IrCl2(PH2Ar)] in CH2Cl2 at low temperatures resulted in the novel fused‐ring systems 17 (Ar=Mes*) and 20 (Ar=Mes), with dimeric [{Cp*IrPAr}2] being the likely intermediate. Intramolecular CH bond activation induced by steric factors is considered to be the driving force for the irreversible formation of 17 and 20. ONIOM calculations suggest this arises because of the large steric congestion in [{Cp*IrPAr}2], which forces it toward a more reactive planar structure that is apt to rearrange.

Nucleophilic Phosphinidene Complexes: Access and Applicability

“…[51] Lammertsma and co-workers showed that dehydrohalogenation of primary phosphine complex 48 a with the strong phosphazene base tert-butylimino-tri(pyrrolidino)phosphorane (BTPP, pK b % 26) in the absence of a ligand gave 18-electron complex 57 and one-half equivalent of the dimer [{Cp*IrCl 2 } 2 ] (58, Scheme 17 a). [52] Phosphinidene 57 , as identified by its 31 P NMR spectrum (d = 366 and À126 ppm), and suggests that the first dehydrohalogenation is faster than the second one. The reaction appears to be sensitive to the size of the substituent on phosphorus, as the smaller Mes group gave the intermediate dimetallacycle 61, resulting from dimerization of [Cp*(Cl)Ir = P(H)Mes], and subsequently on dehydrohalogenation dimer 62 (Scheme 17 c).…”

Phosphinidene-bridged binuclear complexes

“…Lammertsma and co-workers reported the dehydrohalogenation of the mononuclear iridium complexes [IrCl 2 Cp*(PH 2 Ar)] (Ar = Mes, Mes*) using the strong phosphazene base BTPP (tert-butylimino-tri(pyrrolidino)phosphorane) (Scheme 17) [43]. The outcome of these reactions, however, was critically dependent on several experimental factors such as the substituent size, temperature and stoichiometry.…”

“…Thus, for the bulky PH 2 Mes* phosphine, addition of a two-fold excess of BTPP at room temperature gave the mononuclear phosphinidene [IrCp*(PMes*)(PH 2 Mes*)], while the addition of 1.5 equivalent of base at lower temperature (ca. 200 K) yielded instead the dinuclear phosphinidene/phosphanyl evolves upon addition of further base or on raising the reaction temperature to generate the phosphinidene complex 33, following from a selective C-H bond activation in a putative bis(phosphinidene) intermediate [Ir 2 Cp* 2 (μ-PMes*) 2 ] [43]. In contrast, no phosphinidene complexes could be identified for the Mes-substituted complex, and a double C-H activation product was isolated instead, this suggesting in situ generation of the corresponding bis(phosphinidene) complex which, however, could be neither detected.…”

Nucleophile Phosphinidenkomplexe: Synthese und Anwendungen

“…Lammertsma und Mitarbeiter berichteten, dass bei der Dehydrohalogenierung des primären Phosphankomplexes 48 a mit der starken Phosphazen‐Base tert ‐Butyliminotri(pyrrolidino)phosphoran (BTPP, p K b ≈26) in Abwesenheit eines Liganden der 18‐Elektronen‐Komplex 57 und das Dimer 1/2 [{Cp*IrCl 2 } 2 ] ( 58 , Schema ) entstehen 52. Es wurde angenommen, dass das Phosphiniden 57 aus der Vorstufe [Cp*IrPMes*] durch Abspaltung von PH 2 Mes* entsteht.…”