Preparation and reactivity of η⁶-pyridine tricarbonyl chromium complexes

Abstract

Complexation of 2,6-bistrimethylsilylpyridine followed by desilylation generates y6-pyridinetricarbonylchromium which undergoes regioselective deprotonation-methylation to give 2-methylpyridinetricarbonylchromium and regioand stereo-selective nucleophilic additions of alkyl-lithiums to generate, after methylation, N-methyl-exo-2-al kyl-l,2-di hydropyridinetricarbonylchromium complexes.

The coordination chemistry of organo-hydride donors: new prospects for efficient multi-electron reduction

“…[235][236][237][238][239][240][241][242] For example, Davies et al report addition of diisobutyl aluminium hydride or alkyl lithium reagents to tricarbonyl(Z 6 -pyridine)chromium (55) to selectively afford the corresponding 1,2-dihydropyridine complexes, 56 (Scheme 24). [235][236][237] In contrast to the s-dihydropyridine complexes presented above, the p-bonded 1,2-dihydropyridines are far poorer reducing agents than when 'free' due to the overall electron-withdrawing effect of the bound metal center. Indeed, complex 56 was sufficiently stable to be isolated using chromatography in air.…”

Preparation of tricarbonyl(η6-pyridine)chromium(0) complexes

“…However, addition of water with the tetrabutylammonium fluoride trihydrate at -78 "C and stirring the solution at room temperature in the dark for 1. 5 h led, after evaporation of solvent and flash chromatography (eluting with ether), to tricarbonyl(q6-pyridine)chromium(o) 1 (86%) as a light and air-sensitive yellow crystalline solid which could be recrystallised from isopentane and stored in the dark at -20 "C under an inert atmosphere.…”

Tricarbonyl(pyridine)chromium complexes: conversion into tricarbonyl(dihydropyridine)chromium complexes via regio- and stereo-selective nucleophilic addition reactions

“…121 "C (decomp. ); vmaX/cm-' 1957, 1881 and 1845 (CO); 6,m,Ph),5.81 (1 H,dt,J 1.5 and 4.6,5.46 (1 H,dd,J 5.8 and 7.6,5.38 (1 H,d,J4.6,4.45 (1 H,d,J 5.8,4.06 (1 H, dt, J 1.5 and 7.6, 4-H) at 2.58 (3 H,s,; m/z 307 (M+) (Found: C,58.4;H,4.6;N,4.3. C,,H,,CrNO3 requires C,58.6;H,4.3;N,4.6%).…”

“…122 "C (decomp. ); v,,,/cm-' 1945,1869 and 1831 (CO); 6, 7.30- 7.09 (5 H,m,Ph),m,4.37 (1 H,d,J 5.5,4.06 (1 H, ddd, J 1.8, 2.0 and 7.7, 3-H) (100 mg, 0.437 mmol) was treated with butyllithium (0.4 ml, 0.56 mmol) and methyl iodide (0.2 ml, excess) according to the standard procedure (eluent: 3 : 1) to give 15 as red needles from CH2C1,-hexane (50 mg, 35%); m.p. 96 "C; v,,,/cm-' 1960,1879 and 1842 (CO); 6, 5.59 (1 H, d, J5.5, 5-H) exo-2-tert-Butyl-N,6-dimethyl-1,2-dihydropyridine-(tricarbony1)chromium 16.-Tricarbonyl(2-methylpyridine)chromium 14 (100 mg, 0.437 mmol) was treated with tertbutyllithium (0.3 ml, 0.5 mmol) and methyl iodide (0.2 ml, excess) according to the standard procedure (eluent: 3 : 1) to give 16 as orange-red needles from CH,Cl,-hexane (92 mg, 70%); m.p.…”