Unexpected Metal-Induced Isomerisms and Phosphoryl Migrations in Pt(II) and Pd(II) Complexes of the Functional Phosphine 2-(Bis(diphenylphosphino)methyl)-oxazoline

Abstract

The reaction of the functional diphosphine 1 [1 = 2-(bis(diphenylphosphino)methyl-oxazoline] with [PtCl(2)(NCPh)(2)] or [PdCl(2)(NCPh)(2)], in the presence of excess NEt(3), affords [Pt{(Ph(2)P)(2)C···C(···NCH(2)CH(2)O)}(2)] ([Pt(1(-H)-P,P)(2)], 3a) and [Pd{(Ph(2)P)(2)C···C(···NCH(2)CH(2)O)}(2)] ([Pd(1(-H)-P,P)(2)], 3b), respectively, in which 1(-H) is (oxazoline-2-yl)bis(diphenylphosphino)methanide. The reaction of 3b with 2 equiv of [AuCl(tht)] (tht = tetrahydrothiophene) afforded [Pd(1(-H)-P,N)(2)(AuCl)(2)] (4), as a result of the opening of the four-membered metal chelate since ligand 1(-H), which was P,P-chelating in 3b, behaves as a P,N-chelate toward the Pd(II) center in 4 and coordinates to Au(I) through the other P donor. In the absence of a base, the reaction of ligand 1 with [PtCl(2)(NCPh)(2)] in MeCN or CH(2)Cl(2) afforded the isomers [Pt{(Ph(2)P)(2)C═C(OCH(2)CH(2)NH)}(2)]Cl(2) ([Pt(1'-P,P)(2)]Cl(2) (5), 1' = 2-(bis(diphenylphosphino)methylene)-oxazolidine) and [Pt{(Ph(2)P)(2)C═C(OCH(2)CH(2)NH)}{Ph(2)PCH═C(OCH(2)CH(2)N(PPh(2))}]Cl(2) ([Pt(1'-P,P)(2'-P,P)]Cl(2) (6), 2' = (E)-3-(diphenylphosphino)-2-((diphenylphosphino)methylene)oxazolidine]. The P,P-chelating ligands in 5 result from a tautomeric shift of the C-H proton of 1 to the nitrogen atom, whereas the formation of one of the P,P-chelates in 6 involves a carbon to nitrogen phosphoryl migration. The reaction of 5 and 6 with a base occurred by deprotonation at the nitrogen to afford 3a and [Pt{(Ph(2)P)(2)C···C(···NCH(2)CH(2)O)}{Ph(2)PCH═COCH(2)CH(2)N(PPh(2))}]Cl ([Pt(1(-H)-P,P)(2'-P,P)]Cl (7)], respectively. In CH(2)Cl(2), an isomer of 3a, [Pt{Ph(2)P)(2)C···C(···NCH(2)CH(2)O)}{Ph(2)PC(PPh(2))═COCH(2)CH(2)N}] ([Pt(1(-H)-P,P)(1(-H)-P,N)] (8)), was obtained as a side product which contains ligand 1(-H) in two different coordination modes. Complexes 3b·4CH(2)Cl(2), 4·CHCl(3), 6·2.5CH(2)Cl(2), and 8·CH(2)Cl(2) have been structurally characterized by X-ray diffraction.

Synthesis, Structure, and Optical Properties of Pt(II) and Pd(II) Complexes with Oxazolyl- and Pyridyl-Functionalized DPPM-Type Ligands: A Combined Experimental and Theoretical Study

“…3 The bonding parameters of the ligand 1 −H are consistent with the diphosphine and diphosphinomethanide limiting forms shown in Scheme 7. 3 For simplicity, in the following we shall represent the phosphorus−metal bonds involving this anionic ligand by simple lines.…”

“…The site of protonation in both 3a and 3b was clearly established by 1 H NMR spectroscopy (CD 3 CN) with the appearance of NH resonances at 6.57 and 6.62 ppm, respectively. These signals disappear in CD 3 OD solution as a result of H/D exchange.…”

“…1,2 Because of our combined interest in the synthesis and applications of such P,N ligands in coordination chemistry and catalysis 2−4 and in short-bite diphosphine ligands such as bis(diphenylphosphino)methane, Ph 2 PCH 2 PPh 2 (dppm), bis(diphenylphosphino)amine, Ph 2 PNHPPh 2 (dppa), and their derivatives, which are well-known for their ability to stabilize di-or polynuclear complexes and clusters 5 and allow, e.g., their anchoring inside nanoporous membranes, 6 we decided to introduce an oxazoline moiety as a substituent on the PCP carbon of the dppm ligand. 3 The coordination behavior of 2-{bis(diphenylphosphino)-methyl}oxazoline, (Ph 2 P) 2 CHCNCH 2 CH 2 O (1) (Scheme 1), has barely been examined. 4 Comparative studies performed with 2-{bis(diphenylphosphino)methyl}pyridine, (Ph 2 P) 2 CH(2-C 5 H 4 N), could shed light on the possible influence of the different basicities of the N-heterocycles on the chemistry and properties of their metal complexes.…”

“…3 However, depending on the solvent in which the deprotonation of 1 was carried out, unexpected changes in the coordination modes of (oxazolin-2-yl)-bis(diphenylphosphino)methanide (1 −H ) were observed, as it can even exhibit both P,P and P,N chelating modes within the same complex (Scheme 6). 3 The bonding parameters of the ligand 1 −H are consistent with the diphosphine and diphosphinomethanide limiting forms shown in Scheme 7. 3 For simplicity, in the following we shall represent the phosphorus−metal bonds involving this anionic ligand by simple lines.…”

“…3 were readily protonated in the solid state by HBF 4 2+ also forms upon reaction of 1 with [PtCl 2 (NCPh) 2 ] in MeCN or CH 2 Cl 2 . 3 In 3a and 3b, ligand 1′ has a protonated heterocyclic nitrogen (Scheme 9), in contrast to its tautomer 1, which is the only form of the uncoordinated ligand that has been isolated and observed spectroscopically. The site of protonation in both 3a and 3b was clearly established by 1 H NMR spectroscopy (CD 3 CN) with the appearance of NH resonances at 6.57 and 6.62 ppm, respectively.…”