James E. Lyons

SELECTIVE HOMO DIELS‐ALDER CYCLOCODIMERIZATION OF OLEFINS, ACETYLENES, AND CONJUGATED ACYCLIC DIENES WITH NORBORNADIENE USING A SOLUBLE COBALT CATALYST*

The homogeneous transition metal-catalyzed codimerization of norbornadiene with unsaturated substrates has been the subject of extensive investigation for more than a decade.” Many different dimerization pathways have been observed, including those which give [2 + 21 or [2 + 2 + 21 cross-addition products as well as simple vinyl addition products.2b Often a single transition metal complex will catalyze many different pathways, giving rise to a complex mixture of products.2’ In other instances, a particular metal complex may catalyze selective codimerization reactions; however, the reaction pathway may differ from one unsaturated substrate to another.2a Situations of these types have given rise to a rich and diverse dimerization chemistry but may also limit the predictive capability and, in some instances, the preparative utility of the catalytic process. Moreover, in addition to possible problems related to selectivity and predictability, the transition metal complexes used to date have proven to be effective Diels-Alder catalysts only for codimerization of norbornadiene with olefins or acetylenes that bear strongly electron withdrawing groups or that are part of a highly strained system. This paper describes the use of a cobalt complex formed by reducing [Co(acac),] with diethylaluminum chloride (DEAC) in the presence of the bidentate ligand system, bis[ 1,2diphenylphosphino]ethane (DIPHOS), as a catalyst for the selective codimerization of norbornadiene with conjugated acyclic dienes, olefins, and simple acetylenes without electron withdrawing groups, to give a family of similar fused-ring hydrocarbons in which the norbornadiene segment has been transformed into the nortricyclenic ring system. A mechanistic scheme is postulated which rationalizes the analogous codimerization be

Homogeneous catalytic hydrogenolysis of the C–O bond: the selective reduction of cyclic carboxylic acid anhydrides to γ-lactones catalysed by [RuCl2(Ph3P)3]

avior of a variety of unsaturated substrates with norbornadiene in the presence of the cobalt complex.

Selective homo-Diels–Alder addition of acetylenic hydrocarbons to norbornadiene catalysed by a cobalt complex

[RuCl2(Ph3P)3] is an efficient catalyst for the selective partial hydrogenation of carboxylic acid anhydrides; γ-lactones are formed from succinic and phthalic anhydrides.

Group VIII metal complexes as catalysts for halogen exchange between alkyl halides

A cobalt complex, formed by reducing [Co(acac)3](Hacac = acetylacetone) with diethyl-aluminium chloride in the presence of the bidentate ligand bis(1,2-diphenylphosphino)ethane, is an active catalyst for the selective [2+2+2] cycloaddition of acetylenic hydrocarbons RCCH (R = alkyl, H, or aryl) to norbornadiene.

Stereoselective cobalt-catalysed [2 + 2 + 2] cross-addition of norbornadiene and norbornene

Several co-ordinatively unsaturated d6 and d8 group VIII metal complexes are efficient catalysts for halogen exchange reactions between a variety of alkyl halides.

Ruthenium-cobalt carbonyl catalysts for the dealkoxyhydroxymethylation of acetals to form glycol ethers

A cobalt complex, formed by reducing [Co(acac)3](Hacac = acetylacetone) with diethyl-aluminium chloride in the presence of the bidentate ligand bis(1,2-diphenylphosphino)ethane, is an active catalyst for the stereoselective [2 + 2 + 2] cycloaddition of norbornene to norbornadiene.