Syntheses of bispyrazolyl monotriazolyl heteroscorpionate platinum(IV) complexes including an unusual Pt-CH2CH2-Pt bridge

Abstract

Scorpionate ligands provide the benefit of hemilability while minimizingcomplete dissociation of the ligand. Previous investigations into Tp′PtL n X m complexes[Tp′= hydridotris(3,5-dimethylpyrazolyl)borate]revealed the importance of hemilabilityas the Tp′ligand facilitates Pt(II/IV) interconversions. Here we discuss the synthesis and metalation of a series of asymmetric scorpionate ligands bearing two pyrazolyl rings and one triazolyl ring. In addition to utilizing triazole donor arms with differing substituents, we also compareoctahedral structures of Pt(IV) complexes with P=O and C-H and B-H caps at the pole of the facial tridentate umbrella.Oxidation from Pt(II) to Pt(IV) with electrophilic reagents, simple acids and acid chlorides, leads to isomers in some cases, and the binding properties of the various donor arms dictatethe stereochemistry of the products. Investigations into the reactivity of heteroscorpionate tridentate ligandsbound to platinum(II)led to C-Cl activation reactions with methylene chloride and 1,2dichloroethane. Isolation of a dinuclear platinum complex bridged by an ethylene unit produced

Facial–Meridional Isomerization and Reductive Elimination in [(R2P-o-C6H4)2N]PtMe3 (R = Ph, iPr)

“…Consistent with the solution structures deduced from NMR spectroscopy, X-ray studies of these trimethylplatinum­(IV) complexes (Figure and Table ) revealed them to be distorted octahedral species having facial and meridional configurations. The [R-PNP]­M configuration in fac -[Ph-PNP]­PtMe 3 and fac -[ i Pr-PNP]­PtMe 3 is similar to that in fac -[Ph-PNP]­Ir­(η 4 -COD) but different from that in the majority of known PNP pincer complexes. ,, The mer -PtMe 3 configuration in mer -[Ph-PNP]­PtMe 3 and mer -[ i Pr-PNP]­PtMe 3 is unique in view of the popular fac -PtMe 3 core − ,− ,, in six-coordinate trimethylplatinum­(IV) complexes. Diagnostically, two of the methyl ligands in mer -[Ph-PNP]­PtMe 3 and mer -[ i Pr-PNP]­PtMe 3 are trans-disposed, having C–Pt–C angles of 178.1(2)° and 176.1(4)°, respectively.…”

“…Among these, reactions in toluene by the lithiation route (method A) were the least successful. The fac -PtC 3 configuration of fac -[Ph-PNP]­PtMe 3 and fac -[ i Pr-PNP]­PtMe 3 is reminiscent of what is known for six-coordinate trihydrocarbylplatinum­(IV) complexes, − ,− ,, including those containing monodentate or chelating ligands having one nitrogen-donor and two phosphorus-donor atoms such as fac -PtEt 2 (CH 2 Ph)­(PMe 3 ) 2 (NCS), fac -[PtMe 2 (CCSiMe 3 )­(dmpe)­(solv)]­(OTf) (solv = NCMe, py), fac -PtMe 3 (dppbz)­(NHSO 2 R) [dppbz = o -bis­(diphenylphosphino)­benzene; R = 4-C 6 H 4 n Bu, 4-tolyl], fac -[PtMe 3 (dppe)­(py)]­OTf, fac -[PtMe 3 (Ph 2 PCH 2 C­( t Bu)NNC­( t Bu)­CH 2 PPh 2 )]­PF 6 , fac -PtMe 3 (Ph 2 PCHC­( t Bu)­NNC­( t Bu)­CH 2 PPh 2 ), fac -[PtMe 3 (PMe 2 Ph) 2 (NCMe)]­I, and fac -PtMe 3 (PMe 2 Ph) 2 (NO 2 )…”

“…Trimethylplatinum­(IV) complexes are popular. − ,− ,, It is well-documented that the stereochemistry of trimethylplatinum­(IV) complexes is always facial. , The possibility of these complexes, as well as their lower and higher homologues such as those containing the PtMe 2 R fragment (R = H, Et), having a meridional geometry has long been overlooked largely because of the strong trans influence of an alkyl or a hydride ligand. Research on the fac – mer isomerization of six-coordinate trialkylplatinum­(IV) complexes prior to reductive elimination is therefore unexplored.…”