Organic reactions involving transition metals. Part V. Nucleophilic attack on co-ordinated dienes by carboxylate ions and a rearrangement reaction of a co-ordinated norbornenyl group

Abstract

The complexes (diene) MCI, (diene = norbornadiene, dicyclopentadiene, M = Pd, Pt; diene = cyclo-octa-1,5-diene, hexa-1.5-diene, M = Pt) react with silver carboxylates, AgOzCR (R = CH,, CH,CI, CH,F, C,H,), to give in most cases the complexes [(RCO,-alkenyl) MO,CR], in which one double bond of the diene has undergone nucleophilic attack. In three cases the monomeric products (diene) Pt(O,CR), are obtained (diene = norbornadiene, R = CH,CI, CH,F; diene = cyclo-octa-l,5-diene, R = CH,F). The n.m.r. spectra of some of the norbornadiene derivatives have been examined and a controversy over band assignments is resolved. The norbornadiene derivatives react with triphenylphosphine to give dimeric products [( RC0,C7H8) M(0,CR) PPh,], in which the organic ligand has rearranged to a nortricyclene system. THE reactions of the complexes (diene)MCl, (diene = norbornadiene, dicyclopentadiene, cyclo-octa-l,5diene, M = Pd, Pt) with nucleophiles have been widely studied. The nucleophiles examined to date are hydroxide,2 a l k~x i d e s ,~-~ carboxylate~,~ carbanions,s-10 and amines.6y10911 It is thus now established that the nucleophile attacks one double bond of the diene at an exo-position, i.e. the attack results in the trans-addition of the metal and the nucleophile across the double bond, in contrast to the cis-addition thought to occur with mono-olefins. A recent report has suggested that tram-addition can sometimes occur with mono-olefins.12 Evidence for the stereochemistry of the addition to the dienes has come from the crystal structure13 of the compound [ ( MeOCl,Hl,)PdC1], and from examination of the products of degradation reaction^.^^^^ Confirmation of the exo-configuration of the complexes has also been sought on the basis of n.m.r. spectra, but two groups of workers give conflicting assignm e n t~.~~~~The reactions of a range of (diene)MCl, complexes with carboxylate ions have now been studied; the reactivity of the complex is very dependent on the structure of the diene, and on the nucleophilicity of the anion. The n.m.r. spectra of the norbornadiene and dicyclopentadiene derivatives have been re-examined and definitive band assignments are now given, The reactions of triphenylphosphine with the compounds prepared during these studies have also been investigated; in the case of the norbornadiene derivatives, skeletal rearrangement of the ligand has been observed. , to cyclo-octa-1,5-diene are reported 25 in systems. and D.