R.Thomas Honeyman

The synthesis of tripodal nitrogen donor ligands and their characterization as PdIIMe2 and PdIIIMe derivatives

New tripod ligands containing pyridin-2-yl (py), N-methylimidazol-2-yl (mim), and pyrazol-l-y1 (pz) groups have been made by addition of 2-bromopyridine to deprotonated (py)(mim)CH2 or (mim)2CH2 to form (py)2(mim)CH and (py)(mim)2CH, or by simple condensation reactions of (pz)2CO with (mim)CHO or (py)CHO to form (pz)2(mim)CH and (pz)2(py)CH. The ligands may have general application in coordination and organometallic chemistry, especially bis(pyrazol-lyl)(pyridin-2-yl)methane [(pz)2(py)CH], which can be readily synthesized and is an unsymmetrical tripod closely related to (pz)3CH and (py)3CH. Dimethylpalladium( II) and methyl(iodo)palladium(II) complexes of the ligands have been isolated, and compared with complexes of (pz)3CH, (py)3CH, and (pz)4C.

Trimethylpalladium(IV) chemistry. Conformational and fluxional effects in related palladium(IV) and platinum(IV) complexes of flexible bidentate nitrogen donor ligands

Abstract Iodomethane reacts with palladium(II) complexes PdMe 2 (L 2 ), where L 2 is a flexible nitrogen donor ligand such as 1,1-bis(pyridin-2-yl)ethane [(py) 2 CHMe], to form unstable trimethylpalladium(IV) complexes characterized as fac -PdIMe 3 (L 2 ) by comparison of their variable temperature 1 H NMR spectra with those of stable trimethylplatinum(IV) analogues. The complexes fac -MIMe 3 {(py) 2 CHMe} occur as mixtures of isomers, with the chelate ring having the CH group adjacent to iodine in one isomer and adjacent to the methyl group trans to iodine in the other isomer. Complexes containing pyrazol-1-yl (pz) or N -methylimidazol-1-yl (mim) donors, fac -MIMe 3 (L 2 ) [L 2 = (pz) 2 CH 2 , (pz)(mim)CH 2 , and (py)(pz)CH 2 ] undergo fluxional behaviour involving inversion of the six-membered chelate rings.

Synthesis and isomerism of neutral and cationic dimethylplatinum(IV) complexes. Crystal structure of the bis(pyrazol-1-yl)(thien-2-yl)methane complex PtI2Me2{(pz)2(thi)CH-N,N′}

Abstract The reaction of [PtMe2(SEt2)]2 with tripodal nitrogen donor ligands and iodine in dichloromethane gives diiododimethylplatinum(IV) complexes, PtI2Me2{(pz)2(L) CH-N,N′}, in which the N,N′-bidentate ligands are trans to the cis-PtMe2 group and have one uncoordinated donor group. The bis(pyrazol-1-yl)(thien-2-yl)methane complex, PtI2Me2{(pz)2(thi)CH-N,N′}, has PtI bond lengths of 2.6199(7) and 2.6649(6) A for the trans-PtI2 group, and PtC bond lengths of 2.070(7) and 2.097(9) A, and PtN bond lengths of 2.181(5) and 2.192(6) A. Complexes of (pz)2(L)CH [L = N-methylimidazol-2-yl (mim), pyridin-2-yl (py)] exist as a mixture of isomers, with an isomer ratio as expected for a random distribution of coordinated pz and L donor groups, 2:1 for 2pz: (pz + L) coordination. The complexes of (pz)3CH, (pz)2(mim)CH, and (pz)2(py)CH are converted into [PtIMe2{(pz)2(L)CH-N,N′,N″}]I on heating, and the cations of the unsymmetrical tridentate ligands (pz)2(L)CH (L = py, mim) also exist as isomers. The isomers have the donor group L trans to a methyl or iodo group, where the ratio (L trans to Me):(L trans to I) is 2:1 for L = py (as expected for a random distribution of isomers) and 1:1 for L = mim.

Structural studies of complexes containing cycloplatinated tris(pyrazol-1-yl)methane

Abstract Cyclometallation at the C(5) position of one ring of tris(pyrazol-1-yl)methane occurs on dissolution of PtMe 2 {(pz) 3 CH} in 3,5-dimethylpyridine, to form the platinum(II) complex PtMe{(pz) 2 (C 3 H 2 N 2 )-CH- N , C }(3,5-Me 2 py) ( 1b ). Structural studies of 1b , and the related complexes PtMe{(pz) 2 (C 3 H 2 N 2 )-CH- NC }( N -methylimidazole) ( 1c ) and PtMe{(pz) 2 (C 3 H 2 N 2 CH- N , C }{PPh 2 ( o -MeOC 6 H 4 )} ( 1d ) show that these complexes have square planar geometry with cis -organic groups, with the cyclometallated group having one pyrazole ring uncoordinated. The complexes PtMe{(pz) 2 (C 3 H 2 N 2 )CH- C }(L 2 ) [L 2 = 2PPh 3 ( 2a ), 2PEtPh 2 ( 2b ), Ph 2 PCH 2 CH 2 PPh 2 ( 2c )] have a similar geometry at platinum(II); the metallated ligand is present as a [C] − donor with two uncoordinated pyrazole rings. In 2a , 2b , and 2c , there are short Pt⋯H contacts at ~ 2.7 A for the methine proton of the cyclometallated ligand.

Oxidation of organoplatinum(II) and -palladium(II) complexes by water. The X-ray structure of the trimethylpalladium(IV) complex fac-[PdMe3{tris(pyrazol-1-yl)borate}] formed on oxidation of a dimethylpalladium(II) reagent

Diphenyl{tris(pyridin-2-yl)methanol}platinum(II) reacts with water in acetone to form the platinum(IV) complex [PtPh2(py)3COH(OH)]-[OH]· nH2O (n ∼ 1). In contrast, the palladium(II) species [PdMe2-{(py)3COH}] and [PdMeR{tris(pyrazol-1-yl)borate}]− (R = Me, Ph) react with water to form a mixture of PdIV and PdII complexes in reactions involving both oxidation and methyl group transfer. The PdIV complexes fac-[PdMCe{(py)3COH}]+ and fac-[PdMe2R{(pz)3-BH}] (R = Me, Ph) have been identified as products, together with methylpalladium(II) and phenylpalladium(II) species, and the structure of fac-[PdMe3{(pz)3BH}] determined by X-ray crystallography.

Conformational studies in palladium (IV) and platinum (IV) chemistry. Crystal structure of the 1,1-bis(pyrazol-l-yl)- ethane complex fac-PtIMe3(pz)2CHMe-N, N′

Abstract The reaction of iodomethane with the 1,1-bis(pyrazol-1-yl)ethane complex PtMe 2 (pz)2CHMe- N,N ′ gives the platinum(IV) complex fac -PtIMe 3 (pz) 2 CHMe- N,N ′, which has been fully characterized, by, among other means, an X-ray structural study. The analogous palladium(IV) complex has also been prepared by a similar reaction in (CD 3 ) 2 CO at — 30°C, and the two complexes exhibit similar 1 H NMR spectra. For the palladium(IV) species, however, reductive elimination of ethane occurs above — 30°C to give PdIMe(pz) 2 CHMe- N,N ′. The 1 H NMR spectra of the platinum(IV) and palladium(IV) complexes show that they are present in one configuration in solution, and large downfield shifts of the methine C H CH 3 resonance, compared with the same proton in MMe 2 (pz) 2 C4H Me- N,N ′, are consistent with a conformation of the six-membered chelate ring that places the methine proton adjacent to the iodine atom. The octahedral platinum(IV) complex adopts this configuration in the solid state, with I ⋯ H = 3.1 A The 1 H NMR and structural studies support earlier assignments of solution behaviour for platinum(IV) and palladium(IV) complexes of related ligands, e.g. (pz)(py)CH 2 and (py) 2 CHMe (py = pyridin-2-yl), and confirm the influence of hydrogen … halogen interactions on 1 H NMR spectra of octahedral complexes of this type.

Trimethylpalladium(IV) complexes of flexible bidentate ligands. Conformational and fluxional effects in related Me3PdIV and Me3PtIV systems

Abstract A comparison of variable temperature 1H NMR spectra for stable complexes fac-Me3Pt(L2)I with low temperature spectra obtained after addition of iodomethane to Me2Pd(L2) allows assignment of structure for unstable organopalladium(IV) complexes of the flexible bidentate ligands (py)2CHMe and (py)(pz)CH2 (py = pyridin-2-yl, pz = pyrazol-1-yl), together with the first comparison of conformational effects and fluxional processes for organo-palladium(IV) and -platinum(IV) systems. Oxidative addition of CD3I at −50°C occurs with scrambling of CD3 and Me positions in fac-Me2(CD3)Pd(L2)I, but for the platinum analogues the CD3 and iodo ligands remain trans until scrambling occurs on warming to ca. −10°C.