Aryloxycarbonylcarbene Complexes of Bis(oxazolinyl)pyridineruthenium as Active Intermediates in Asymmetric Catalytic Cyclopropanations

Abstract

Abstract:The reaction of [RuCl,(pybox)-(C,H,)] (1) (pybox = 2,6-bis[(4S)-isopropyloxazolin-2'-yl]pyridine) and 2,6-ditert-butyltolyl diazoacetate (4) (DBT-DA) in benzene at 50°C gave a stable 2,6 -di -tert -butyltolylcarbonylcarbeneruthenium complex 5 in 94% yield. The structure of 5 was characterized by NMR spectroscopy. 2,6-Diisopropylphenyl diazoacetate (6) and 2,4,6-trimethylphenyl diazoacetate (7) also gave the corresponding carbene complexes 9 and 10, respectively. Asymmetric carbene transfer from the carbene complexes to styrene resulted in formation of the trans isomer of phenylcyclopropanecarboxylates 2 with high enantioselectivity : 2 was obtained as the sole product in 80% yield (55% ee) from 5 at 80 "C and in 82 % yield (97 YO ee) from 9 at 60 "C; from 10 at 40 "C, a mixture of 2 and 3 in a ratio of 97:3 was formed in 91 740 yield (97% ee for 2 and 99 % ee for 3). After the carbene transfer reaction, the ethylene complex 1 could be regenerated and isolated by treatment of the reaction mixture under an ethylene atmosphere. The carbene complexes 9 and 10 (2 mol%) exhibited catalytic activity in the asymmetric cyclopropanation of styrene with the corresponding diazoacetates.

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

“…The former falls in the Ru=C length range of 1.806(3)-1.876 (3) , whereas the latter is considerably larger than the Ru=C À C angle of % 1258 found for the Ru=CR…”

“…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.…”

“…[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.…”

“…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-…”

Alkane Catalytic Functionalization by Carbene or Nitrene Insertion Reactions

“…A series of Fe, Ru and Os carbene complexes have been reported by the groups of Collman [31], Woo [32][33][34], Che [35][36][37], Simonneaux [38] (Scheme 6.6b). Nishiyama (Scheme 6.6c) [39] and Bianchini (Scheme 6.6d) [40] independently reported the formation of ruthenium and osmium carbene complexes with pybox and triphosphine ligands, respectively. Mezzetti has employed a PNNP ligand to detect a ruthenium-carbene complex (Scheme 6.6e) [41] involved in the imine aziridination reaction.…”