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Isocyanate‐ and Isothiocyanate‐Derived Ru IV ‐Based Alkylidenes: Synthesis, Structure, and Activity
Author(s) -
Kumar P. Santhosh,
Wurst Klaus,
Buchmeiser Michael R.
Publication year - 2009
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200900099
Subject(s) - chemistry , isocyanate , metathesis , ruthenium , romp , thiocyanate , ligand (biochemistry) , isothiocyanate , medicinal chemistry , polymer chemistry , catalysis , polymerization , organic chemistry , polymer , polyurethane , biochemistry , receptor
The synthesis and characterization of a series of isocyanate‐ and isothiocyanate‐derived second generation Grubbs–Hoveyda‐type ruthenium–alkylidene complexes, that is, [Ru(NCO) 2 (IMesH 2 )(CH‐2‐(2‐PrO)‐C 6 H 4 )] ( 1 ), [Ru(NCO) 2 (1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(=CH‐2‐(2‐PrO)‐C 6 H 4 )] ( 2 ), [Ru(NCS) 2 (IMesH 2 )(CH‐2‐(2‐PrO)‐C 6 H 4 )] ( 3 ), and [Ru(NCS) 2 (1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(CH‐2‐(2‐PrO)‐C 6 H 4 )] ( 4 ), and their activity in various metathesis reactions are described. Compounds 1 – 4 were prepared by reaction of the parent complexes [RuCl 2 (IMesH 2 )(CH‐2‐(2‐PrO)C 6 H 4 )] ( 5 ) (IMesH 2 =1,3‐bis‐(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene) and [RuCl 2 (1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(CH‐2‐(2‐PrO)‐C 6 H 4 )] ( 6 ) with silver cyanate and thiocyanate, respectively. The X‐ray structure of 1 was determined, confirming the isocyanate‐type bonding of the ligand. The isothiocyanate‐type bonding in 3 and 4 was unambiguously confirmed by IR and 13 C NMR spectroscopy. The isocyanate‐derived complexes 1 and 2 were found to be excellent catalysts for the ring‐opening metathesis polymerization (ROMP) of cis ‐cycloocta‐1,5‐diene (COD). Both 1 and 2 yielded poly(COD) with a trans ‐content of about 80 %. First‐order kinetics with unprecedentedly high rate constants of polymerization ( k p =0.068 and 0.26 s −1 , respectively) were observed. Compounds 3 and 4 were also active initiators for the ROMP of COD, however, they generated poly(COD) with a cis ‐content of 80 and 67 %, respectively. Complexes 1 and 2 also showed good catalytic activity in cross‐metathesis (CM) reactions. Finally, 1 – 4 were also found to be excellent catalysts for the regioselective cyclopolymerization of diethyl 2,2‐dipropargylmalonate (DEDPM), resulting in poly(DEDPM) almost entirely based on five‐membered repeat units, that is, cyclopent‐1‐ene‐1,2‐vinylenes.