Reactions of [(PPh 3) 2Pt(η 3-CH 2CCPh)] + with oxygen nucleophiles and chemistry of resultant [(PPh 3) 2Pt(η 3-CH 2C(OR)CHPh)] + complexes

Abstract

The η 3-allenyl/propargyl complex [(PPh 3) 2Pt(η 3-CH 2CCPh)]OTf ( 1OTf) undergoes addition reactions with a number of oxygen nucleophiles in CH 2Cl 2 solution at ambient temperature. With H 2O, it yields the binuclear oxygen-bridged η 3-allyl [{(PPh 3) 2Pt(η 3-CH 2CCHPh)} 2O](OTf) 2 ( 2(OTf) 2). With primary and secondary alcohols, it rapidly affords the η 3-(2-alkoxyallyl) complexes [(PPh 3) 2Pt(η 3-CH 2C(OR)CHPh)]OTf (R=Et ( 3OTf), i-Pr ( 4OTf), CH 2CMe 3 ( 5OTf), CH 2CHCH 2 ( 7OTf)), whereas with tertiary alcohols, in slower reactions, it gives both 2(OTf) 2 and [(PPh 3) 2Pt(η 3-CH 2C(OR)CHPh)]OTf (R=CMe 3, C(Me) 2Et ( 6OTf)). There is no reaction at ambient temperature between 1OTf and phenols; however, 1OTf and PhOH afford [(PPh 3) 2Pt(η 3-CH 2C(OPh)CHPh)]OTf ( 8OTf) in the presence of NEt 3. Competition studies reveal the following reactivity order, attributed to steric effects: Me 3CCH 2OH(1.0)< i-PrOH(1.2)<EtOH(2.1)<MeOH(4.3). The η 3-(2-alkoxyallyl) complexes react with NaOMe to yield the η 3-oxatrimethylemethane product (PPh 3) 2Pt(η 3-CH 2C(O)CHPh) ( 10), which was also obtained by reaction of 2(OTf) 2 with two equivalents of NaOMe and of 1OTf with NaOH. Complex 10 undergoes conversion to the appropriate [(PPh 3) 2Pt(η 3-CH 2C(OR)CHPh)] + with [Et 3O]PF 6, (MeO) 2SO 2 and MeI. The η 3-(2-allyloxyallyl) 7OTf reacts with (PPh 3) 2Pt(C 2H 4) to give 10 and [(PPh 3) 2Pt(η 3-CH 2CHCH 2)]OTf; thermolysis of 7OTf in toluene at reflux furnishes [(PPh 3) 2Pt(η 3-CH 2CHCH 2)]OTf, whereas heating in benzene–chloroform affords [(PPh 3) 2Pt(η 3-CH 2C(OCHCHMe)CHPh)]OTf ( 11OTf), which results from isomerization of OCH 2CHCH 2 to OCHCHMe. Reaction pathways have been suggested for a number of the aforementioned transformations. All new complexes were characterized by a combination of elemental analysis, FAB mass spectrometry and 1H-, 13C{ 1H}- and 31P{ 1H}-NMR spectroscopy. They were assigned structures in which the η 3-allyl oxygen and Ph groups are syn from the 1H-NMR spectra.