Please use this identifier to cite or link to this item: http://hdl.handle.net/1783.1/1477

Hydride and acetylene chemistry of cyclopentadienyl group 8 metal complexes

Authors Ng, Weng-Sang
Issue Date 1998
Summary The monohydride complexes CpFeH(P-P) (P-P = dppe and dppp) were synthesized by reactions of CpFeCl(P-P) with NaBH4. Protonation of CpFeH(P-P) with HBF4Et2O produced the molecular dihydrogen complexes [CpFe(η2-H2(P-P)]BF4. The dihydrogen complexes were thermally unstable in solution. Treatment of CpOsBr(P-P) (P-P = dppm, dppe and dppp) with NaOMe in methanol gave the corresponding monohydride complexes CpOsH(P-P). Protonation of CpOsH(P-P) with HBF4Et2O at -78 ℃ gave a mixture of dihydride complexes cis-[CpOsH2(P-P)] BF4 and trans-[CpOsH2(P-P)] BF4. At room temperature in dichloromethane solutions, [CpOsH2(dppm)]BF4 exists as a mixture of cis and tram isomers in a ratio of 10: 1, [CpOsH2 (dppe)]BF4 exists as a mixture of cis and tram isomers in a ratio of 1:70, and [CpOsH2(dppp)]BF4 adopts only the trans geometry. The pseudo-aqueous pKa values of the [CpOsH2(PR3) 2)]BF4((PR[subscrip 3])2 = (PPh3)2, dppm, dppe, and dppp) series have been determined in dichloromethane. The pseudo-aqueous pKa values indicate that the acidities of trans-[CpOsH2(P-P)] BF4(P-P = dppm, dppe, dppp) decrease as the size of the chelating ring increases. cis-[CpOsH2(dppm)] BF4 has been found to be less acidic than cis-[CpOsH2(dppe)] BF4 For the relative acidities of cis and transisomers in equilibrium, it has been shown that the major tautomer is always the weaker acid. The pseudo- aqueous pKa values of the osmium complexes are consistently larger than those of the corresponding ruthenium analogs. Protonation of Cp*RuH(COD) with HBF4Et2O at -78 ℃ produced [Cp*Ru(η2-H2)(COD)]BF4. The dihydrogen complex was thermally unstable and decomposed to [Cp*Ru(η[to the power of 6]-COT)]BF4, on warming up to room temperature. The previously unknown hydride Cp*RuH(NBD) was synthesized from the reaction of [Cp*Ru(H2O)(NBD)]BF4 with sodium formate in THF. Reaction of Cp*RuH(NBD) with HBF4Et2O produced a mixture of nortricyclene and the novel bimetallic complex [(Cp*Ru)2(μ-H)(μ-C5H5CH=CHHagostic)] BF4. The bimetallic complex was unstable and decomposed in solution. Among the decomposed products, two were identified as [(Cp*Ru)2(μ-CpCH2CH3)] BF4 and [(Cp*Ru)2(μ-Cp*RuC5H4CHHagostic CH3)](BF4)2. Protonation of the structural related complex RuHCl(NBD)(PPh3)2, with HBF4.H2O gave norbornene and a mixture of polyaqua complexes. Treatment of Cp*RuCl(dppm) with NaBPh4 in methanol in air produced the dioxygen complex [CpRu(η2-O2)(dppm)]BPh4 which was characterized by X-ray crystallography. Exposure of acetone solutions of [Cp*RuH2(dppm)]BF4 to air led to the formation of [Cp*Ru(η2-O2)(dppm)]BF4 and and [Cp*Ru(η2-O2) ((K-P,O)Ph2CH2P(=O)Ph2)]BF4 in approximately 1:4 ratio. A series of dihydrido-silyl complexes with the formula trans-{Cp*RuH2[(K-P,Si)Ph2 PCH2P(OSiRR')Ph2)]}BPh4 (RR' = HPh, Ph2, Et2) were synthesized by reactions of [Cp*Ru(η2-O2)(dppm)]BPh4 with 1° and 2° silanes. Reaction of HC≡CCH(OH)C≡CH with coordinated unsaturated d6 complexes [Cp*Ru(dppe)]+ gave the C5H2-bridged bimetallic complex [Cp*(dppe)Ru=C=C=CH-CH=C=Ru(dppe)Cp*](BF4)2. Deprotonation of the C5 H2-bridged bimetallic complex by neutral alumina led to the formation of the C5H- bridged complex [Cp*(dppe)Ru=C=C=CH-C≡C-Ru(dppe)Cp*]BF4, The analogous C5H-bridged complexes [Cp(PPh3)2,Os=C=C=CH-C[≡C- Os(PPh3)2Cp]BF4 and [Cp(dppe)Fe=C=C=CH-C≡C-Fe(dppe)Cp] BF4 were synthesized similarly. The structure of [Cp(PPh3)2)Os=C=C= CH-C≡C-Os(PPh3)2)Cp]BF4 was confirmed by X-ray crystallography and showed the bridging C5H ligand to be a delocalized π-system. Reaction of [Cp*(dppe)Ru=C=C=CH-C≡C-Ru(dppe)Cp*]BF4 with acetone in the presence of KOBut produced the neutral complex Cp*(dppe)RuC≡C-CH( CH2COMe)C[≡C-Ru(dppe)Cp*. The [2+2+2] cycloaddition reactions have been studied by using [Cp*Ru(H2O)(NBD)]BF4 and phenyl-functionalized acetylenes. Treatment of [Cp*Ru(H2O)(NBD)]BF4 with 1 equiv. of diphenylacetylene gave the π-arene complex [Cp*Ru(η[to the power of 6]-Ph2C2(C7H8)] BF4. Analogous complex [Cp*Ru(η[to the power of 6]-PhCH3 (C7H8)]BF4 was obtained by using methylphenylacetylene. The above two complexes contain deltacyclene ligands which was formed by [2+2+2] cycloaddition of the acetylene with the coordinated NBD.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 1998
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