Effective Control of Ligation and Geometric Isomerism: Direct Comparison of Steric Properties Associated with Bis-mesityl and Bis-diisopropylphenyl m-Terphenyl Isocyanides

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• 作者：Treffly B. Ditri ; Brian J. Fox ; Curtis E. Moore ; Arnold L. Rheingold ; Joshua S. Figueroa
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：September 7, 2009
• 年：2009
• 卷：48
• 期：17
• 页码：8362-8375
• 全文大小：1234K
• 年卷期：v.48,no.17(September 7, 2009)
• ISSN：1520-510X

文摘

A synthetic procedure for the sterically encumbered m-terphenyl isocyanide CNAr^Dipp2 (Dipp = 2,6-diisopropylphenyl) is presented. In comparison to the less encumbering m-terphenyl isocyanide ligand CNAr^Mes2, the steric attributes of the flanking Dipp groups effectively control the extent of CNAr^Dipp2 ligation to monovalent Cu and Ag centers and zero-valent Mo centers. Direct structural comparisons of Cu(I) and Ag(I) complexes of both CNAr^Dipp2 and CNAr^Mes2 are made. It was found that only two CNAr^Dipp2 ligands are accommodated by monovalent Cu and Ag centers, whereas three CNAr^Mes2 units can readily bind. As demonstrated by both ¹H NMR and FTIR spectroscopic studies, addition of a third equivalent of CNAr^Dipp2 to [(THF)b>2b>Cu(CNAr^Dipp2)b>2b>]OTf in Cb>6b>Db>6b> solution results in slow isocyanide exchange. However, rapid isocyanide exchange is observed when an additional equivalent of CNAr^Dipp2 is added to (TfO)Ag(CNAr^Dipp2)b>2b>. Three CNAr^Mes2 ligands react smoothly with fac-Mo(CO)b>3b>(NCMe)b>3b> to afford the octahedral complex fac-Mo(CO)b>3b>(CNAr^Mes2)b>3b>, which can be converted irreversibly to the mer isomer upon heating in solution. Contrastingly, addition of CNAr^Dipp2 to fac-Mo(CO)b>3b>(NCMe)b>3b> results in a mixture of both the tetracarbonyl and the tricarbonyl complexes trans-Mo(CO)b>4b>(CNAr^Dipp2)b>2b> and trans-Mo(NCMe)(CO)b>3b>(CNAr^Dipp2)b>2b>, respectively, in which the encumbering CNAr^Dipp2 ligands are in a trans-disposition. Ultraviolet irradiation of the preceding mixture in NCMe/Etb>2b>O under an argon flow provides exclusively the tricarbonyl complex trans-Mo(NCMe)(CO)b>3b>(CNAr^Dipp2)b>2b>. Addition of free CNAr^Dipp2 to trans-Mo(NCMe)(CO)b>3b>(CNAr^Dipp2)b>2b> does not result in the binding of a third isocyanide unit by the Mo center as determined by ¹H NMR spectroscopy. Treatment of trans-Mo(NCMe)(CO)b>3b>(CNAr^Dipp2)b>2b> with the Lewis base pyridine (py) affords the complex fac,cis-Mo(py)(CO)b>3b>(CNAr^Dipp2)b>2b> as determined by X-ray diffraction. Notably, the encumbering nature of the CNAr^Dipp2 units forces a cis Cb>isob>−Mo−Cb>isob> angle of about 100°.