Ring Closure Kinetics of Bidentate Hemilabile P,N and P,S Ligands on a Platinum(II) Complex

Abstract

Complexes of the type cis-[PtPh 2 (CO)(η 1 -P−N)] and cis-[PtPh 2 (CO)(η 1 -P−S)], where bidentate phosphorus−nitrogen and phosphorus−sulfur ligands are bound to the metal centre in a monodentate fashion [P−N = Ph 2 PC 5 H 4 N (Ph 2 PPy), Ph 2 P(CH 2 ) 2 C 5 H 4 N (ppye), Ph 2 P(o-C 6 H 4 )NMe 2 (PNMe 2 ), Ph 2 P(CH 2 ) n NMe 2 (n = 2, 3, i.e., peNMe 2 and ppNMe 2 ) and P−S = Ph 2 P(CH 2 ) 2 SEt (P−SEt), Ph 2 P(CH 2 ) n SPh (n = 1, 2, i.e., P−CH 2 SPh and P−SPh)], were prepared in situ by reaction of the hybrid ligands with cis-[PtPh 2 (CO)(SEt 2 )]. In each case, the first observed process was the fast substitution of diethyl sulfide by the phosphanyl group leading to the monosubstituted ring-open cis-[PtPh 2 (CO)(η 1 -P−X)] (X = N or S) complexes, which were characterised in solution by 1 H and 31 P{ 1 H} NMR spectroscopy. These initially formed species undergo a slow ring closure process with extrusion of carbon monoxide and formation of the chelate [PtPh 2 (P−X)] products, except in the case of the short-bite Ph 2 PPy and P−CH 2 SPh ligands and of ppNMe 2 , where ring closure was not observed. The chelate complexes were isolated as solids

Kinetic Evaluation of Ligand Hemilability in Transition Metal Complexes

“…The substitution reactions of the homoditopic S–S ligands of [Pt(Ph) 2 {κ 2 ‐( S , S )‐Ph 2 S(CH 2 ) n SPh 2 }] ( n = 2,3) by a diphosphane were found to proceed according to Equation (2), indicating the formation of a monodentate κ 1 ‐ S transient species 36. Parallel first‐ and second‐order kinetics were also observed for the acid‐promoted ring openingand displacement by chloride of the bidentate chelateligand from dichloro[pyridine‐2‐(α‐methoxymethanolato)]gold(III) 14d…”

Synthesis, characterization, reactivity and theoretical studies of ruthenium carbonyl complexes containing ortho-substituted triphenyl phosphanes

“…It can be expected that the methoxy phosphane resembles the thiomethoxy phosphane and thus assume that aminophosphane is also more basic than thiomethoxy phosphane. Recent studies on ring closure kinetics of bidentate hemilabile (np) and (sp) ligands on platinum [42] showed that the ring closure rate constant is faster than the rate constant for the opening, suggesting that the equilibrium between chelated and non-chelated complexes is shifted towards the chelated species. This means that once the ring is formed (fast rate) cleavage of the metal-nitrogen or metal-sulphur bond is difficult (slow rate).…”

Mono‐ and Trinuclear Tripodal Platinum(II) Chelated Complexes Containing a Pyridine/Sulfoxide Based Anchoring Framework

“…6a or 9 ), together with the final chelated species and free dimethyl sulfoxide (diagnostic signal at 2.5 ppm). Any attempts to identify by 1 H NMR spectroscopy, even at low temperatures, the presence of other intermediate open‐ring species or, in the case of the trans ‐platinum(II) complex Pt2 , other coordination isomers were unsuccessful 20. This means that the kinetic rate constant for the sulfoxide ring‐closure is too high compared with that of the substitution process of the pyridine moiety, leading to the conclusions that the open‐ring species once formed is rapidly converted into the corresponding chelated species 20,21.…”

“…Platinum(II) Complexes Derivatives: The platinum(II) compounds cis ‐[PtMe 2 (Me 2 SO) 2 ] ( Pt1 )19 and trans ‐[PtMeCl(Me 2 SO) 2 ] ( Pt2 )20 were prepared according to already published methods and were purified by several crystallizations from a 1:1 CH 2 Cl 2 /Et 2 O mixture (v/v).…”