Syntheses, structures and reactivity of the group 6 and 7 metal complexes containing chelating nitrogen donor ligands and metal-ligand multiple bonds

by Lee, Fu-wa

Abstract (Summary)
(Uncorrected OCR) Abstract of thesis entitled ?YNTHESES, STRUCTURES AND REACTIVITY OF THE GROUP 6 AND 7 METAL COMPLEXES CONTAINING CHELATING NITROGEN DONOR LIGANDS AND METAL-LIGAND MULTIPLE BONDS?submitted by Lee Fu Wa for the degree of Doctor of Philosophy at the University of Hong Kong in September, 1997. ____________________________________________________________________ [Cr(CRMe3)Cl2]+ (CRMe3=meso-2,3,7,11,12-pentamethyl-3,7,11,17- tetraazabicyclo[11.3.1]-heptadeca-1(17),13,15-triene), [Cr(CRMe3)Cl(H2O)]2+, [Cr(CRMe3)Cl(CH3CN)]2+ and [Cr(CRMe3)(N3)(OH)]+ are prepared. Upon addition of PhI=O to solutions of [Cr(CRMe3)Cl(CH3CN)]2+ and [Cr(CRMe3)Cl(H2O)]2+ respectively in CH3CN, the UV-visible absorption spectra of the two mixtures show similar isosbestic spectral changes attributed to the formation of [CrV(CRMe3)Cl(O)]2+. Addition of Ph3P causes the immediate recovery of [Cr(CRMe3)Cl(CH3CN)]2+ as the isosbestic changes are reversed. Irradiation of [Cr(CRMe3)(N3)(OH)]+ in acetonitrile with UV-visible light gives an azide-free product, the FAB-MS of which shows a molecular ion peak indicative of ([CrV(CRMe3)(N)]ClO4)+. The UV-visible spectra of [Cr(CRMe3)Cl2]+, [Cr(CRMe3)Cl(H2O)]2+ and [Cr(CRMe3)Cl(CH3CN)]2+ measured in water are similar to that of [Cr(CRMe3)(H2O)2]3+. Results from the conductivity measurement show that in water, [Cr(CRMe3)Cl2]+, [Cr(CRMe3)Cl(H2O)]2+ and [Cr(CRMe3)Cl(CH3CN)]2+ behave as 3:1 electrolytes. The species which exists in water is likely to be the di-aquo complex [Cr(CRMe3)(H2O)2]3+. [Cr(CRMe3)Cl(H2O)]2+ and [Cr(CRMe3)Cl(CH3CN)]2+ are both found to give a reversible oxidation couple at +1.11 V vs. SCE in aqueous solutions at pH=1 which is assigned to Cr(III)/(IV). iii The bis(imido) complexes [(TACN)M(NtBu)2Cl]+ (M=Cr, Mo; TACN=1,4,7-triazacyclononane) and their 1,4,7-trimethyl derivatives are prepared, the crystal structures of which reveal the trans influence of the imido group. These d0 species display a quasi-reversible couple at potentials 0.86 - 1.20 V vs. Cp2Fe+/0 in acetonitrile assignable to a imido ligand-centred oxidation. (Me3TACN)Mo(CO)3, 1,4,7-Tri((S)-2-methylbutyl)-1,4,7-triazacyclononane (L*) and L*Mo(CO)3 are synthesized. (Me3TACN)Mo(CO)3 and L*Mo(CO)3 show reversible oxidation couples at -0.26 V and -0.24 V vs. Cp2Fe+/0 in CH3CN respectively which are assigned to MoI/0. The comparable electronic effect of Me3TACN and L* in this system is therefore implied. [(Me3TACN)2Mn2(?O)(?OCOCH3)2]2+ is prepared and found to mediate aziridination of styrene, methylstyrene, cis- and trans-stilbene, 1,1-diphenylethene and norbornene by PhI=NTs in CH2Cl2 at 25 ?. The nitrene transfer to cis- and trans-stilbene is found to be stereoselective to exclusively give the trans-aziridine product. [(Me3TACN)(CO)2M CPh]+ (M=Mo, W) and [(TACN)(CO)2Mo CPh]+ are prepared. [(Me3TACN)(CO)2M CPh]+ (M=Mo, W) exhibit a reversible reduction couple at -2.15 V vs Fe2Cp+/0 and an irreversible wave at 0.77 V vs Fe2Cp+/0, which are ascribed to a reduction centred at the phenyl ring and oxidation of the terminal CO respectively. Treatment of Cl(CO)2py2Cr CPh with Me3TACN in THF yield the dinuclear complex [(Me3TACN)2Cr2(?OH)(? iv OCOCH2Ph)2]3+ as the major product. Coupling of the carbyne and carbonyl ligands is apparently involved. A minor product isolated in 2 % yield displays carbonyl stretching bands at 1980 and 1901 cm-1 and a molecular cluster at m/z 368 corresponding to [(Me3TACN)(CO)2Cr CPh]+. [Cl(?2-Ppy3)(CO)2W CPh)] (Ppy3=tris(2-pyridyl)phosphine), [(?3- Ppy3)(CO)2M CPh]+ (M=Mo, W), [(?3-HCpy3)(CO)2W CPh]+ (HCpy3=tris(2-pyridyl)methane), [(TTCN)(CO)2W CPh]+ (TTCN=1,4,7-trithiacyclononane), [(P3)(CO)2W CPh]+ (P3=1,1,1-tris(diphenylphosphinomethyl)ethane) and [Cl(dppbz)2M CPh] (M=Mo, W; dppbz =1,2-bis(diphenylphosphino)benzene) are isolated. The crystal structures of [(Me3TACN)(CO)2Mo CPh]+, [(Me3TACN)(CO)2W CPh]+, [(?3-HCpy3)(CO)2W CPh]+, [(?3- Ppy3)(CO)2W CPh]+, [(P3)(CO)2W CPh]+ and [Cl(?2-Ppy3)(CO)2W CPh)] revealed the trans influence of the phenyl carbyne moiety. Excitation of [(Me3TACN)(CO)2W CPh]+, [(?3-HCpy3)(CO)2W CPh]+, [(?3- Ppy3)(CO)2M CPh]+ (M=Mo,W), [(P3)(CO)2W CPh]+ and [Cl(dppbz)M CPh] (M=Mo, W) at 330 nm in dichloromethane give intense orange to red emission. The emissive state is likely to be 3[(dxy)1(dp*)1]. v
Bibliographical Information:


School:The University of Hong Kong

School Location:China - Hong Kong SAR

Source Type:Master's Thesis

Keywords:metal complexes ligands


Date of Publication:01/01/1998

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