A phosphomide based PNP ligand, 2,6-{Ph₂PC(O)}₂(C₅H₃N), showing PP, PNP and PNO coordination modes

Abstract

A new class of PNP pincer ligands, pyridine-2,6-diylbis(diphenylphosphino)methanone, 2,6-{Ph2PC(O)}2(C5H3N) (1) (hereafter referred to as "bis(phosphomide)"), was prepared by the reaction of picolinoyldichloride with diphenylphosphine in the presence of triethylamine. The bis(phosphomide) 1 shows symmetrical PNP, unsymmetrical PNO and simple bidentate PP coordination modes when treated with various transition metal precursors. The reaction between 1 and [Ru(p-cymene)Cl2]2 in a 1 : 1 molar ratio yielded a binuclear complex [Ru2Cl4(NCCH3)(p-cymene){2,6-{Ph2PC(O)}2(C5H3N)}] (2) containing an unsymmetrical PNO pincer cage around one of the ruthenium centers, whereas the second ruthenium is bonded to the other phosphorus atom along with cymene and two chloride atoms. Symmetrical pincer complexes [RuCl(NCCH3)2{2,6-{Ph2PC(O)}2(C5H3N)}](ClO4) (3), [Ru(η(5)-C5H5){2,6-{Ph2PC(O)}2(C5H3N)}](OTf) (4) and [RhCl{2,6-{Ph2PC(O)}2(C5H3N)}] (5) were obtained in the respective reactions of 1 with [RuCl(NCCH3)2(p-cymene)](ClO4), [Ru(η(5)-C5H5)Cl(PPh3)2] and [Rh(COD)Cl]2. Group 10 metal complexes [NiCl{2,6-{Ph2PC(O)}2(C5H3N)}](BF4) (6), [PdCl{2,6-{Ph2PC(O)}2(C5H3N)}]ClO4 (7) and [PtCl{2,6-{Ph2PC(O)}2(C5H3N)}]ClO4 (8) were obtained by transmetallation reactions of in situ generated Ag(I) salts of 1 with Ni(DME)Cl2 or M(COD)Cl2 (M = Ni, Pd and Pt). The reactions between 1 and CuX or [Cu(NCCH3)4](BF4) produced mononuclear complexes of the type [CuX{2,6-{Ph2PC(O)}2(C5H3N)}] (9, X = Cl; 10, X = Br; 11, X = I), [Cu(NCCH3){Ph2C(O)}2(C5H3N)}](BF4) (12) and [Cu{Ph2C(O)}2(C5H3N)}2](BF4) (13). Similarly, the silver complexes [AgX{2,6-{Ph2PC(O)}2(C5H3N)}] (14, X = ClO4; 15, X = Br) were obtained by the treatment of 1 with AgClO4 or AgBr in 1 : 1 molar ratios. Treatment of 1 with AuCl(SMe2) in 1 : 1 and 1 : 2 molar ratios produced mono- and binuclear complexes, [AuCl{2,6-{Ph2PC(O)}2(C5H3N)}] (16) and [Au2Cl2{2,6-{Ph2PC(O)}2(C5H3N)}] (17), in good yield. The structures of ligand 1 and complexes 2, 5 and 17 were confirmed using single-crystal X-ray diffraction studies. DFT calculations were carried out to gain more insights into the structure and bonding features as well as feasibility of some key chemical transformations.

On the Geometrical Stability of Square‐Planar Platinum(0) Complexes That Bear a PNP‐Pincer‐Type Phosphaalkene Ligand (Eind2‐BPEP)

“…We have confirmed that [Pt(L)(Eind 2 -BPEP)] complexes (2)(3)(4)(5)(6) possess ad istinct tendency to adopt as quare-planar configuration aroundt he Pt center,i rrespectiveo ft he electronic properties of L. Although the strong p-acceptor CO ligand produces flexibility towards distortion, the optimized structure of model complex 6 sm as well as the X-ray structure of complex 6 showedt hat planarity was preserved aroundt he Pt center.T he highly adaptable electronics tructure of the Eind 2 -BPEP ligand and the characteristic d 9 s 1 electron configurationo fP tt hat arise from relativistic effectsh ave emerged as the origins of the unusual coordination structure. p-Accepting properties of Ls ignificantly affect the HOMO levels, which led to remarkable color variationso ft he complexes in the near-infrared region.…”

“…All manipulations were carried out under an itrogen atmosphere. Eind 1,3,3,5,5,7,2,3,5,6, [3] and [Pt(cod) 2 ] [12] were prepared according to literature procedures. The other chemicals were obtained from commercial suppliers and used without purification.…”

“…Either they are significantly distorted (A) [1] or they change to at hreecoordinate species to relieve the distortion (B). [2] On the other hand, we recently found that the Pt 0 complex [Pt(PPh 3 )(Eind 2 -BPEP)] (1)( Eind = 1,1,3,3,5,5,7,7-octaethyl-1,2,3,5,6,7-hexahydros-indacen-4-yl;B PEP = 2,6-bis(1-phenyl-2-phosphaethenyl)pyridine), which bears aP NP-pincer-type phosphaalkene ligand (Eind 2 -BPEP), adopts ah ighly planar configuration around the Pt center (t 4 = 0.11). [3,4] Although there have been af ew precedents of formal d 10 complexes with as quare-planar or distorted-square-planar configuration, all of them are dianionic species of d 8 metals, which are stabilized by electrostatic interactions with Li + or Na + ions at the apical positions.…”

“…31 PNMR data and selectedb ondlengths ()a nd angles (8)for X-ray crystals tructures of [Pt(L)(Eind 2 -BPEP)](2)(3)(4)(5)(6). [a] …”

Aroylphosphanes: Base‐Free Synthesis and Their Coordination Chemistry with Platinum‐Group Metals

“…The coordination chemistry of such “phosphomide” ligands is, nonetheless, scant and largely restricted to groups 6–8 (Cr, Mo,, W, Mn, Re, Fe, Ru) with an emphasis on the first‐row metals. A limited range of group 9 complexes has been described with “Cp′RhCl 2 ” (Cp′ = Cp, Cp*) and “Cp*IrCl 2 ” fragments; however, trans ‐Rh(CO)(L) 2 Cl (L = PH 2 {C(O)Me}, PPh 2 {C(O)C 7 F 15 }, PPh 2 {C(O) p ‐An}) and [Rh{κ 2 ‐ P , P ‐C 6 H 3 N{PC(O)PPh 2 } 2 ‐2,6}Cl][13a] are the only low‐valent group 9 complexes known.…”