Transition metal complexes of the pyridylphosphine ligand o-C₆H₄(CH₂PPy₂)₂

Abstract

The synthesis and coordination behaviour of the pyridylphosphine ligand o-CH(CHPPy) (Py = 2-pyridyl) are reported. The phosphine selenide was synthesised and the J value of 738 Hz indicates the phosphorus atoms have a similar basicity to PPh. The ligand reacts with platinum(ii) and palladium(ii) complexes to give simple diphosphine complexes of the type [MX(PP)] (M = Pt, X = Cl, I, Me, Et; M = Pd, X = Cl, Me). When the ligand is reacted with chloromethyl(hexa-1,5-diene)platinum the [PtClMe(PP)] complex results, from which a series of unsymmetrical platinum complexes of the type [PtMeL(PP)] (L = PPh, PTA, SEt and pyridine) can be made. This enabled the comparison of the cis and trans influences of a range of ligands. The following cis influence series was compiled based on P NMR data of these complexes: Py ≈ Cl> SEt > PTA > PPh. Reaction of [PtClMe(PP)] with NaCH(SOCF) and carbon monoxide slowly formed an acyl complex, where the CO had inserted in the Pt-Me bond. Attempts to achieve P,P,N chelation, through abstracting the chloride ligand in [PtClMe(PP)], were unsuccessful. When the ligand reacted with platinum(0), palladium(0) and silver(i) complexes the bis-chelated complexes [M(PP)] (M = Pt, Pd) and [Ag(PP)] were formed respectively. Reaction of the ligand with [Ir(COD)(μ-Cl)] formed [IrCl(PP)(COD)]. When the chloride ligand was abstracted, the pyridyl nitrogens were able to interact with the iridium centre facilitating the isomerisation of the 1,2,5,6-η-COD ligand to a 1-κ-4,5,6-η-CH ligand. The X-ray crystal structure of [Ir(1-κ-4,5,6-η-CH)(PPN)]BPh confirmed the P,P,N chelation mode of the ligand. In solution, this complex displayed hemilabile behaviour, with the pyridyl nitrogens exchanging at a rate faster than the NMR time scale at room temperature.

(In situ) spectroscopic studies on state-of-the-art Pd(ii) catalysts in solution for the alkoxycarbonylation of alkenes

“…39,[58][59][60] There are various examples in the literature for similar coordination modes in palladium and other transition metal complexes modified by pyridyl and other N-heterocyclic phosphine ligands. [40][41][42][43][44][45][46]64 As observed here, often those complexes do show dynamic fluxionality in solution. [65][66][67][68]…”

“…Interestingly, while the organometallic chemistry and catalytic behaviour of P,N pyridylmonophosphines and pincer type P,N,P ligands were widely studied, there are only a few reports on pyridyldiphosphines of the N,P,P,N or N,N,P,P,N,N type and their respective transition metal complexes. 31,40–46…”

“…Interestingly, while the organometallic chemistry and catalytic behaviour of P,N pyridylmonophosphines and pincer type P,N,P ligands were widely studied, there are only a few reports on pyridyldiphosphines of the N,P,P,N or N,N,P,P,N,N type and their respective transition metal complexes. 31,[40][41][42][43][44][45][46] This study presents a continuation of our preceding work on alkene alkoxycarbonylation by palladium catalysts modified by pyridyl-substituted diphosphines which covered experimental catalytic and kinetic investigation as well as DFT computations on the individual steps of the catalytic cycle. 20 The main focus of this current work is to provide new insights into relevant aspects of those specific palladium based catalytic systems incorporating N,P,P,N type pyridyldiphosphine ligands by the characterisation of Pd complexes and possible intermediates in solution using liquid phase (in situ) spectroscopic techniques.…”

Tridentate κ3-P,P,C iridium complexes: influence of ligand saturation on intramolecular C–H bond activation

“…Equally unusual is the 1,2,3,5-η 3 ,η 1 -C 8 H 12 binding motif – which, to our knowledge, is unprecedented; 39 more common is the 1,2,3,6-η 3 ,η 1 -C 8 H 12 binding motif, as observed by us and others. 30,40–45 The above qualities are showcased in the solid-state structure of (±)-3 , namely: a –(CH 2 )(CH)(CH)– linker arm, with C–C bond lengths of 1.335(9) and 1.49(1) Å and a slight Ir(1)–C(linker) contraction of 2.062(7) Å cf. , 2.165(8) and 2.164(3) Å for (±)-1 and (±)-2 , respectively.…”