Cycloneophylplatinum Chemistry: A New Route to Platinum(II) Complexes and the Mechanism and Selectivity of Protonolysis of Platinum–Carbon Bonds

Abstract

A new route to cycloneophylplatinum­(II) complexes is reported and the selectivity of protonolysis of the platinum–aryl and −alkyl bonds has been determined. Reaction of [PtCl2(SMe2)2] with neophylmagnesium chloride gives the binuclear cycloneophylplatinum­(II) complex [Pt2(CH2CMe2C6H4)2(μ-SMe2)2], 1, which is shown to exist as a mixture of syn and anti isomers. Complex 1 reacts reversibly with SMe2 to give [Pt­(CH2CMe2C6H4)­(SMe2)2], 2, and irreversibly with bidentate ligands NN = 3,4,7,8-tetramethyl-1,10-phenanthroline (phen*) or 4,4′-di-t-butyl-2,2’bipyridine (bubipy) to give the corresponding complexes [Pt­(CH2CMe2C6H4)­(phen*)], 3, and [Pt­(CH2CMe2C6H4)­(bubipy)], 4, respectively. Complex 2 reacts with HCl initially by cleavage of the aryl–platinum bond to give mostly trans-[PtCl­(CH2CMe2Ph)­(SMe2)2], which then rearranges to an equilibrium mixture with trans-[PtCl­(C6H4-2-t-Bu)­(SMe2)2], while 3 and 4 react to give [PtCl­(CH2CMe2Ph)­(phen*)] and [PtCl­(CH2CMe2Ph)­(bubipy)], which do not undergo the isomerization reaction. The protonolysis reactions occur by way of a platinum­(IV) hydride complex in each case, and the unusual reactivity of complex 2 is attributed to the ease of dissociation of the Me2S ligands.

Complexes Containing a Phenol–Platinum(II) Hydrogen Bond: Synthons for Supramolecular Self‐Assembly and Precursors for Hydridoplatinum(IV) Complexes

“…Cationic monomethylplatinum(II) complexes, such as [PtMe(SMe 2 )( L1 )]Cl, are also known and they form supramolecular polymers through OH ··· Cl and NH ··· Cl hydrogen bonding, and do not contain OH ·· Pt hydrogen bonds . The new electron‐rich cycloneophylplatinum(II) complexes 1–4 were prepared by reaction of the precursor complex [Pt 2 (CH 2 CMe 2 C 6 H 4 ) 2 (µ‐SMe 2 ) 2 ] with the corresponding ligands L1 – L4 , with displacement of the weakly bound dimethyl sulfide ligands (Scheme ). The new complexes were characterized spectroscopically and complexes 1 , 2 and 3 were shown to contain OH ·· Pt hydrogen bonds by X‐ray structure determinations.…”

“…In each case, the platinum(II) center is square planar with the aryl and pyridyl groups mutually trans . This stereochemistry is expected because it avoids unfavorable steric interactions between the roughly co‐planar aryl and pyridyl groups . However, the main feature of interest is the presence of an OH ··· Pt hydrogen bond in each complex.…”

“…Isomerization of P1 is likely to involve chloride dissociation to regenerate intermediate I1 , followed by rearrangement and recoordination of chloride. The isomerization of the 16‐electron platinum(IV) intermediates is thought to occur by migration of an equatorial group to the vacant axial site while the axial group moves to the vacated equatorial site, by way of a pinched trigonal bipyramidal intermediate , . In this mechanism, I1 can rearrange to I2 or I3 and chloride coordination can then give P2 or P3 .…”

“…The complex [Pt 2 (CH 2 CMe 2 C 6 H 4 ) 2 (µ‐SMe 2 ) 2 ] and ligands L1 – L4 were synthesized according to the literature procedures ,. [10a] MALDI‐TOF mass spectra were collected using an AB Sciex 5800 TOF/TOF mass spectrometer using pyrene or anthracene as the matrix in a 20:1 matrix:substrate molar ratio. Single‐crystal X‐ray diffraction measurements were made using a Bruker APEX‐II CCD diffractometer with graphite‐monochromated Mo‐ K α (λ = 0.71073 Å) radiation.…”

2‐Aminoalkylgold Complexes: The Putative Intermediate in Au‐Catalyzed Hydroamination of Alkenes Does Not Protodemetalate

“…Hydridoplatinum(IV) intermediates were observed experimentally in protonolysis of square planar d 8 Pt(II) complexes, under certain conditions. [45][46][47] However, these d 8 Pt(II) species differ from d 10 Au(I) complexes with regard to the occupied orbitals, i. e. the HOMO, so the analogy may not be relevant. We consider protodeauration via oxidative addition/reductive elimination (S E ox mechanism, M3) to be uncompetitive.…”