Isomers of Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes

Abstract

The library of molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes Mo(N-G)(CHCMe 2 R 1 )(OTf) 2 (NHC) (G = 2,6-Me 2 -C 6 H 3 , 2,6-Cl 2 -C 6 H 3 , 2-CF 3 -C 6 H 4 , 2-tBu-C 6 H 4 , 2,6-iPr 2 -C 6 H 3 , tBu, adamantyl, 1-phenylcyclohexyl, 1phenyl-3-methylcyclohexyl) was extended to complexes with unsymmetrical (4i) and chiral (4j) imido ligands. New 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes, 4b−d, 4f,g, 4i−k), 1,3-biscyclohexylimidazol-2-ylidene (ICy, 4h, 4l−n), and 1,3,4triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (TPT, 4a, 4e, 4o) complexes were synthesized. Substitution of one triflate in the molybdenum imido alkylidene NHC bistriflate compounds with an alkoxide or a phenoxide afforded complexes Mo(N-G)(CHCMe 2 R 1 )(OTf)(OR 2 )(NHC) (5a−i) and was confirmed to proceed via a selective replacement of one specific triflate. The careful analysis of NMR and single-crystal X-ray data allowed for the determination of solution and solid-state structures. Cis-and trans-OTf isomers of IMes complexes with alkyl-substituted imido ligands, rotamers of TPT-ligated complexes, and syn-/anti-isomers and diastereomers were identified.

Interconversion Rates and Reactivity of Syn- and Anti-rotamers of Neutral and Cationic Molybdenum and Tungsten Imido Alkylidene N-Heterocyclic Carbene Complexes

“…19 F NMR (CD 2 Cl 2 ): δ = −77.08 (s br, 3F, CF 3 ), −77.38 (s br, 3F, CF 3 ), −78.16 (s br, 3F, CF 3 ), −78.78 (s br, 3F, CF 3 ). 13 27 (0.13 g, 0.19 mmol, 1 equiv) was dissolved in n-pentane (10 mL) and a solution of 1,3-diisopropylimidazol-2-ylidene (IiPr, 0.03 mg, 0.19 mmol, 1 equiv) in n-pentane (5 mL) was slowly added at −34 °C. The reaction mixture was stirred for 3 h, then the yellow solid that had formed was filtered off and washed with n-pentane.…”

“…19 F NMR (C 6 D 6 ): δ = −75.22 (m, 6F, CF 3 ), −76.20 (m, 3F, CF 3 ), −76.71 (m, 3F, CF 3 ). 13 C NMR (C 6 D 6 ): δ = 293.9 (CHCPh), 185.1 (CN carbene ), 150.9 (C Aryl ), 149.4 (C Aryl ), 128.7 (C Aryl ), 127.2 (C Aryl ), 127.0 (C Aryl ), 126.3 (br, C�C), 126.1 (C Aryl ), 124.6 (m, CF 3 ), 123.6 (C Aryl ), 122.5 (m, CF 3 ), 122.4 (m, CF 3 ), 117.6 (C Aryl ), 80.7 (m, OCMe(CF 3 ) 2 ), 55.9 (CMe 2 Ph), 53.6 (N−CH), 53.3 (N−CH), 34.1 (CMe 2 Ph), 28.6 (CMe 2 Ph), 27.5 (CH 3 ), 25.1 (CH 3 ), 24.6 (CH 3 ), 22.9 (CH 3 ), 22.7 (CH 3 ), 22.5 (CH 3 ), 18.9 (CH 3 ), 17.3 (CH 3 ). Elemental Analysis (%) Calcd For C 39 H 51 F 12 MoN 3 O 2 : C, 51.04; H, 5.60; N, 4.58; Found: C, 50.99; H, 5.68; N, 4.65.…”

“…2). Catalysts 6, 11 8, 11 9, 11 15, 12 16, 13 17, 12 18, 13 19, 14 20 15 as well as 2,3di(pentoxymethyl)norborn-5-ene (M1) 16 (Figure 2) were prepared according to the literature. UV-Experiments.…”

“…Analysis of the data was performed using the Enhanced Data Analysis program. [Mo(N-CHCMe 2 Ph)(OTf) 2 ],13 catalysts 6, 11 7 13 , 8,11 9, 11 15, 12 16,13 17,12 18,13 19, 14 20 15 were prepared according to the literature.…”

Stereoselective Ring‐Opening Metathesis Polymerization with Tungsten Sulfido Alkylidene N‐Heterocyclic Carbene Complexes

“…In many cases, cis-isotactic (cis-it), trans-isotactic (trans-it), cis-syndiotactic (cisst), or trans-syndiotactic (trans-st) structures are formed virtually selectively. [7,8] More recently, the new class of cationic DOI: 10.1002/macp.202200350 molybdenum and tungsten alkylidene NHC catalysts bearing imido, oxo and sulfido ligands, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] respectively, has been developed. Compared to Schrock-type catalysts, this class of catalysts is characterized by a generally increased tolerance toward oxygen, moisture and functional groups [14,15,29] as well as by higher activities and productivities with turnover numbers exceeding 1.2 million when supported on silica.…”