Alkene metathesis: applications in the synthesis of novel organometallic complexes, and mechanistic investigations. (2008)

Chapter 1 provides an overview on alkene metathesis reaction. Chapter 2 describes a mass spectrometric investigation of the activity of Hoveyda's second generation metathesis catalyst. Reduction of (CD3)2CO with NaBH4 affords 2-propanol-d6 (6-d6, 53%). Treatment of 6-d6 with HBr gives 2-bromopropane-d6 (3-d6, 63%). Subsequent O-alkylation of salicylaldehyde with 3-d6 (Cs2CO3 base) yields 2-isopropoxybenzaldehyde-d6 (4-d6, 60%). Wittig olefination of 4-d6 (Ph3PCH3+ Br&#8722;, t-BuOK) affords 2-isopropoxystyrene-d6 (1-d6, 35%). Nitration of mesitylene-d12 gives 1,3,5-trimethylnitrobenzene-d11 (12-d11, 74%). Catalytic hydrogenation of 12-d11 yields 2,4,6-trimethylaniline-d11 (7-d11, 76%). Condensation of glyoxal with 7-d11 (2 equiv) affords the diimine glyoxal-bis(2,4,6-trimethylphenylimine)-d22 (9-d22, 90%). Treatment of 9-d22 with NaBH4 gives the diamine N,N'-bis(2,4,6-trimethylphenyl)ethylenediamine-d22 dihydrochloride (10-d22, 83%). Reaction of 10-d22 with HC(OEt)3 leads to 1,3-bis(2,4,6-trimethylphenyl)imidazolinium-d22 chloride (2-d22, 84%). Reaction of Ru(=CHPh)(PCy3)2(Cl)2 (13) with 2-d22 (hexanes, t-BuOK) gives Ru(=CHPh)(H2IMes-d22)(PCy3)(Cl)2 (14-d22, 57%). Treatment of 14-d22 with 1-d6 in the presence of CuCl yields (H2IMes-d22)(Cl2)Ru=CH-o-OC6H4(i-Pr-d6) (15-d28, 85%). Mixtures of 15-d28 and its natural abundance analog 15-d0 are utilized in crossover experiments; depending upon conditions, the recovered catalyst can be either unscrambled or a 15-d0/15-d6/15-d22/15-d28 mixture. The latter is consistent with a boomerang mechanism. Chapter 3 describes the synthesis and characterization of gyroscope-like complexes with doubly trans-spanning bis(pyridine) ligands. Reactions of 2,6-NC5H3(CH2Br)2 with CH2=CHCH2MgBr (1.0 M in diethyl ether), and HO(CH2)nCH=CH2 (n = a, 1; b, 2; c, 3; d, 4) in the presence of C6H5CH2N(CH3)3+ Cl&#8722; afford alkene containing pyridines 2,6-NC5H3(CH2CH2CH=CH2)2 (21, 60%), and 2,6-NC5H3(CH2O(CH2)nCH=CH2)2 (22a-d, 45-55%), respectively. Reactions of 3,5-NC5H3(COCl)2 with HO(CH2)nCH=CH2 (n = a, 1; b, 2; c, 3; d, 4; e, 5; f, 6; g, 8) give 3,5-NC5H3(COO(CH2)nCH=CH2)2 (29a-g, 41-90%). Williamson ether syntheses involving 2,6-NC5H3Br2 and HO(CH2)nCH=CH2 (n = a, 1; b, 2) yield 2,6-NC5H3(O(CH2)nCH=CH2)2 (45-55%). Square planar complexes of most of the preceding substituted pyridines are synthesized. Reaction of [RhCl(coe)2]2 (coe = cyclooctene) with 22a gives trans-Rh(Cl)(CO)[2,6-NC5H3(CH2OCH2CH=CH2)2]2 (26%). PtCl2 is treated with 22a,b and 29a,c-g to give trans-PtCl2[2,6-NC5H3(CH2O(CH2)nCH=CH2)2]2 (trans-31a, 88%; trans-31b, 26%) and trans-PtCl2[3,5-NC5H3(COO(CH2)nCH=CH2)2]2 (trans-32a,c-g, 63-94%), respectively. Reactions of trans-(PhCN)2PdCl2 with 29e and 21 afford trans-PdCl2[3,5-NC5H3(COO(CH2)5CH=CH2)2]2 (94%) and trans-PdCl2[2,6-NC5H3(CH2CH2CH=CH2)2]2 (trans-34, 15%), respectively. Treatment of trans-31a,b and trans-32d-g with 13 and subsequent hydrogenation (Pd/C catalyst) gives the gyroscope-like complexes trans-PtCl2[2,6,2',6'-(NC5H3(CH2O(CH2)2n+2OCH2)2H3C5N)] (trans-35a,b, 10-22%) and trans-PtCl2[3,5,3',5'-(NC5H3(COO(CH2)2n+2COO)2H3C5N)] (trans-36d-g, 14-45%), respectively. The reaction of trans-34 with 13 affords trans-PdCl2[2,6,2',6'-(NC5H3((CH2)2CH=CH(CH2)2)2H3C5N)] (trans-37, 55-58%) after column chromatography. Subsequent hydrogenation (PtO2 catalyst) gives trans-PdCl2[2,6,2',6'-(NC5H3((CH2)6)2H3C5N)] (trans-38, 58-62%). The reaction of trans-32c with PhC&#8801;CH, in the presence of CuI, affords trans-Pt(Cl)(C&#8801;CPh)[3,5-NC5H3(COO(CH2)3CH=CH2)2]2 (trans-39c, 18%). The crystal structures of trans-31a, trans-35a, trans-35b, trans-36e, and trans-38 are determined and analyzed. Chapter 4 describes an NMR study of the reactivity of Grubbs' first and second generation metathesis catalysts with alkene-containing pyridines and rhenium complexes. Sequential treatment of (R)-(&#951;5-C5H5)Re(NO)(PPh3)(CH3) ((R)-40) with Ph3C+ PF6– and CH2=CHCH2MgBr (1.0 M in diethyl ether) affords the butenyl complex (R)-(&#951;5-C5H5)Re(NO)(PPh3)(CH2CH2CH=CH2) ((R)-45, 50% after recrystallization). Analogous treatment of (R)-40 with Ph3C+ PF6– and CH2=CHCH2CH2MgBr (0.5 M in THF) gives the pentenyl rhenium complex (R)-(&#951;5-C5H5)Re(NO)(PPh3)(CH2CH2CH2CH=CH2) ((R)-46, 45% after column chromatography). Equimolar quantities of the alkene-containing rhenium complexes (R)-43, (R)-45, and (R)-46, and alkene-containing pyridines 22a, 25b, and 29g are combined with 13 or Ru(=CHPh)(H2IMes)(PCy3)(Cl)2. The reactions are monitored by low temperature NMR. The reaction of (R)-45 (2 equiv) with 13 yields (&#951;5-C5H5)Re(NO)(PPh3)(CH2)2(CH=)Ru(PCy3)2(Cl)2 (49%) in &#8805; 90% purity, as assayed by 31P{1H} NMR. The crystal structure of (R)-46 is determined and analyzed.