Cyclopropanation catalyzed by osmium porphyrin complexes

Abstract

Cyclopropanation of alkenes can be accomplished catalytically2 or stoichiometrically.3 Catalytic systems typically use a diazo reagent as the carbene source and a metal-containing mediator which forms a postulated metal carbene intermediate. Transfer of the carbene fragment from the metal to an alkene produces the cyclopropane product. Despite the wide variety of catalytic cyclopropanation systems, the putative carbene complex has never been isolated or observed in a catalytic system. This is somewhat surprising since the second category of cyclopropanation reactions involves the stoichiometric reaction of isolated car bene complexes with an alkene to form a cyclopropane. None of the isolated carbene complexes show catalytic cyclopropanation activity. Several years ago Callot demonstrated that rhodium porphyrins catalytically cyclopropanated a variety of alkenes in the presence of ethyl diazoacetate.4 Kodadek and co-workers have expanded this work and have attempted to prepare synthetically useful enantioselective catalysts for the formation of cyclopropanes.5 Their approach has been to use rhodium complexes with optically active porphyrins to induce chirality into the product. A similar approach was used for a variety of non-porphyrin copper catalysts.6 Kodadek has shown that the carbon-bound diazonium complex [(TTP)RhC(H)(C02Et)(N2W is an intermediate in the catalytic cyclopropanation of styrene with ethyl diazoacetate.7•8 In addition, kinetic studies suggest that the formation of a rhodium carbene complex is at least partially rate limiting.8 However, this carbene complex has not been isolated or directly observed. We report herein the use of osmium porphyrins as stereoselective cyclopropanation catalysts using ethyl diazoacetate with a variety of alkenes. In addition, our studies show that an isolable carbene complex ((TTP)Os=CHC02Et) is capable of catalytically and stoichiometrically cyclopropanating styrene. Disciplines Chemistry CommentsReprinted ( (Figure 2). Likewise the B-e bonds are shorter than typical single bonds [1.558 A in B(C 2 H 3 h]. 13 Similar evidence has been offered to support delocalization of the two 1r electrons over the three-membered ring and aromatic character for the BC 2 ring in trimesitylborirene.12 Furthermore, the BC 2 rings in BC 2 H 2 and HBC 2 H 2 are seen to be virtually identical. Thus, the u radical site in BC 2 H 2 has no effect on the delocalized 1r bonding in the BC 2 ring. The photolysis of BC 2 H 2 in the near ultraviolet range indicates a strong absorption band in this region, in agreement with trimesitylborirene.13 The photolysis behavior also provides evidence for delocalized bonding as acetylene and ethylene absorb at shorter wavelengths.The appearance of BC 2 H 2 on diffusion and reaction of B atoms at 18 K in solid argon follows similar behavior for B0 2 • 1 These exothermic reactions proceed without activation energy. The BC 2 H 2 radical is the simplest borirene species yet observed and characterized. Further studies are in progress in this laboratory...

Trapping Reactive Metal–Carbene Complexes by a Bis‐Pocket Porphyrin: X‐ray Crystal Structures of RuCHCO2Et and trans‐[Ru(CHR)(CO)] Species and Highly Selective Carbenoid Transfer Reactions

“…[2][3][4] Characterization of these reactive complexes by X-ray crystal analysis has been realized for the M=CR 1 R 2 (R 1 ¼ 6 H and R 2 ¼ 6 H) species. [4a,b,e,h-j] Recently, Simonneaux and co-workers structurally characterized [RuA C H T U N G T R E N N U N G {CHCO 2 (2, 5,10,15,20-tetraphenylporphyrinato(2À)), [5] an M=CHCO 2 R complex kinetically stabilized by a bulky R group.…”

“…[6] To the best of our knowledge, only one M= CHCO 2 Et complex has been structurally characterized in the literature, that is, Werner and co-workers' carbene com-…”

“…[8] Metalloporphyrin-catalyzed alkene cyclopropanation with diazo compounds, including EDA, has received a considerable attention [9] since the pioneering work by Callot and Piechocki. [10] By using simple porphyrin ligand ttp and sterically encumbered porphyrin ligands 5,10,15,20-tetra-A C H T U N G T R E N N U N G mesitylporphyrinato(2À) (tmp) and Haltermans porphyrin 5,10,15,20-tetrakis{(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl}porphyrinato(2À) (D 4 -por*), [11] Collman and co-workers isolated [12] Woo and co-workers isolated [Os- [2] and we observed the formation of [Ru- [13] But characterization of these M=CHCO 2 Et porphyrin complexes by X-ray crystal analysis has not been realized. On the other hand, a wide…”

“…Such reactions of allyl halides with EDA catalyzed by metal complexes are sparse. [24] A proposed mechanism involves attack of metalcarbene intermediates by allyl halides to generate halonium ylides; the latter undergo [2,3]sigmatropic rearrangement to give the observed products. [24] With catalyst [Ru(CO)A C H T U N G T R E N N U N G (tmp)] (0.1 mol %), the reaction of 10 a-c with EDA gave 8 as the major product, with a low 11:8 yield ratio of (0.15-0.43):1.…”

“…Since the isolation of (2À)) by Woo and co-workers [2] and [by Nishiyama and co-workers [3] from the reaction of diazo compounds with metal catalysts, a number of reactive metal-carbene complexes have been isolated or directly observed from such reactions.[2-4] Characterization of these reactive complexes by X-ray crystal analysis has been realized for the M=CR 1 R 2 (R 1 ¼ 6 H and R 2 ¼ 6 H) species.[4a,b,e,h-j] Recently, Simonneaux and co-workers structurally character- 5,10,15,20-tetraphenylporphyrinato(2À)), [5] an M=CHCO 2 R complex kinetically stabilized by a bulky R group.While N 2 CHCO 2 Et (EDA) has been used in numerous studies on metal-catalyzed carbenoid transfer reactions, particularly intermolecular cyclopropanation of alkenes,[1] the corresponding reactive M=CHCO 2 Et intermediates have sparsely been isolated, [2, 4c,d] in contrast to the report of a good number of reactive M=CR 1 R 2 (R 1 ¼ 6 H and R 2 ¼ 6 H) complexes.[6] To the best of our knowledge, only one M= CHCO 2 Et complex has been structurally characterized in the literature, that is, Werner and co-workers' carbene com-[7] which has not been reported to undergo carbenoid transfer with hydrocarbons. Given the effective shielding of the carbene center by bulky 2,6-tBu 2 -4-Me-C 6 H 2 in the structure of [Ru-…”