(Eta(6)-quinoline) and (eta(6)-isoquinoline)' chromium(0) complexes: Synthesis and reactivity

A series of {dollar}etasp6{dollar}-quinoline- and {dollar}etasp6{dollar}-isoquinoline-chromium(0) complexes was prepared for the first time by indirect or direct methods. ({dollar}etasp6{dollar}-Quinoline)-Cr(CO){dollar}sb2{dollar}PPh{dollar}sb3{dollar} (9, 43%) was produced by condensation of ({dollar}etasp6{dollar}-o-aminobenzaldehyde)Cr(CO){dollar}sb2{dollar}PPh{dollar}sb3{dollar} 7 with acetaldehyde in the presence of NaOH. ({dollar}etasp6{dollar}-2-Methylquinoline)Cr((CO){dollar}sb2{dollar}PPh{dollar}sb3{dollar} (8, 70%) was also prepared by condensation of the same complex 7 with acetone. ({dollar}etasp6{dollar}-Isoquinoline)-Cr(CO){dollar}sb2{dollar}PPh{dollar}sb3{dollar} (16, 52%) was produced by reduction of ({dollar}etasp6{dollar}-diethyl homophthalate)Cr(CO){dollar}sb2{dollar}PPh{dollar}sb3{dollar} 20 with DIBAL followed by quenching with aqueous NH{dollar}sb4{dollar}Cl solution and treatment with gaseous ammonia. ({dollar}etasp6{dollar}-2-Methylquinoline)Cr(CO){dollar}sb3{dollar} (2, 75%), ({dollar}etasp6{dollar}-2-(trimethylsilyl)quinoline) -Cr(CO){dollar}sb3{dollar} (22, 6%), ({dollar}etasp6{dollar}-2-(t-butyldimethylsilyl)quinoline) Cr(CO){dollar}sb3{dollar} (24, 65%), ({dollar}etasp6{dollar}-1-methylisoquinoline)Cr(CO){dollar}sb3{dollar} 29, and ({dollar}etasp6{dollar}-1,3-dimethylisoquinoline)-Cr(CO){dollar}sb3{dollar} (32, 40%) were prepared by direct complexation of the corresponding ligands with (CH{dollar}sb3{dollar}CN){dollar}sb3{dollar}Cr(CO){dollar}sb3{dollar}. ({dollar}etasp6{dollar}-Quinoline)Cr(CO){dollar}sb3{dollar} 3 was produced by condensation of ({dollar}etasp6{dollar}-o-aminobenzaldehyde)Cr(CO){dollar}sb3{dollar} 1 with acetaldehyde or direct complexation of quinoline with (CH{dollar}sb3{dollar}CN){dollar}sb3{dollar}Cr(CO){dollar}sb3{dollar}.; The reactivity of {dollar}etasp6{dollar}-quinoline- and {dollar}etasp6{dollar}-isoquinoline-chromium(0) complexes was investigated mainly with respect to scope and limitations of nucleophilic addition. The following conclusion was drawn from the observations made in chapter III: (1) Nucleophiles do not add to the benzene ring in the chromium(0) complexes of quinoline and isoquinoline. (2) The reactivity of anions successful in the addition to ({dollar}etasp6{dollar}-quinoline)chromium(0) complexes ranges from ester enolate to sulfur-stabilized carbanions, which indicates somewhat higher reactivity of ({dollar}etasp6{dollar}-quinoline)chromium(0) complexes compared to free ligands. (3) Several methods of trapping the addition adducts with electrophiles (e.g., CF{dollar}sb3{dollar}CO{dollar}sb2{dollar}H, CH{dollar}sb3{dollar}I, and RCOCI) are available to give chromium(0) complexes of substituted dihydroquinolines and dihydroisoquinolines. (4) Regioselectivity in the nucleophilic addition to chromium(0) complexes of quinoline and isoquinoline is similar to that for the free ligands. (5) Nucleophiles can add to the benzene ring in the chromium(0) complexes of quinoline and isoquinoline when reactive sites of the pyridine ring are blocked (e.g., 1,3-dimethylisoquinoline ligand). (6) Overall double nucleophilic addition to quinoline ligands is possible. The transformation of 2-methylquinoline to 1,4-dihydro-1,2-dimethylquinoline functionalized at C-4 and C-7 was demonstrated by {dollar}pi{dollar}-coordination of 2-methylquinoline to Cr(CO){dollar}sb3{dollar} as a test case. (7) Functionalization of the quinoline ligand with high regioselectivity is possible by metalation and electrophilic trappings of ({dollar}etasp6{dollar}-quinoline) chromium(0) complexes. (Abstract shortened with permission of author.)...