The carboxylate species Mo(NR)(CHCMe2R′)(O2CCPh3)2 (R = various aryl groups or 1-adamantyl; R′ = Ph or Me) have been synthesized by salt metathesis between Mo(NR)(CHCMe2R′)(OTf)2(DME) (OTf = trifluoromethanesulfonate; DME = 1,2-dimethoxyethane) and sodium triphenylacetate. Other carboxylate compounds that have been prepared by this route include Mo(NAr)(CHCMe2Ph)(O2CR′′)2 (Ar = 2,6-i-Pr2C6H3; R′′ = CPh2Me, Si(SiMe3)3) and Na[Mo(NAd)(CHCMe2Ph)(O2CAr′)3] (Ar′ = 2,6-Me2C6H3). Terphenylcarboxylate species Mo(NR)(CHCMe2Ph)(O2CTer)2 (Ter = 2,6-diphenyl-4-methylphenyl or 2,6-diphenyl-4-methoxyphenyl) were prepared through protonolysis of Mo(NR)(CHCMe2R′)(Me2Pyr)2 with TerCO2H, and one of them was characterized through X-ray crystallography. Trimethylphosphine adducts of selected triphenylacetate complexes have been isolated, and the X-ray crystal structure of Mo(NAr′′)(CH-t-Bu)(O2CCPh3)2(PMe3) (Ar′′ = 2-t-BuC6H4) was obtained. Several of the triphenylacetate complexes are active initiators for the regioselective polymerization of diethyl dipropargylmalonate (DEPDM).

Seven bipyridine adducts of molybdenum imido alkylidene bispyrrolide complexes of the type Mo(NR)(CHCMe2R′)(Pyr)2(bipy) (1a–1g; R = 2,6-i-Pr2C6H3 (Ar), adamantyl (Ad), 2,6-Me2C6H3 (Ar′), 2-i-PrC6H4 (AriPr), 2-ClC6H4 (ArCl), 2-t-BuC6H4 (ArtBu), and 2-MesitylC6H4 (ArM), respectively; R′ = Me, Ph) have been prepared using three different methods. Up to three isomers of the adducts are observed that are proposed to be the trans and two possible cis pyrrolide isomers of syn alkylidenes. Sonication of a mixture containing 1a–1g, HMTOH (2,6-dimesitylphenol), and ZnCl2(dioxane) led to the formation of MAP species of the type Mo(NR)(CHCMe2R′)(Pyr)(OHMT) (3a–3g). DCMNBD (2,3-dicarbomethoxynorbornadiene) is polymerized employing 3a–3g as initiators to yield >98% cis,syndiotactic poly(DCMNBD). Attempts to prepare bipy adducts of bisdimethylpyrrolide complexes led to formation of imido alkylidyne complexes of the type Mo(NR)(CCMe2R′)(Me2Pyr)(bipy) (Me2Pyr = 2,5-dimethylpyrrolide; 4a – 4g) through a ligand-induced migration of an alkylidene α proton to a dimethylpyrrolide ligand. X-ray structures of Mo(NAr)(CHCMe2Ph)(Pyr)2(bipy) (1a), Mo(NAriPr)(CHCMe2Ph)(Pyr)(OHMT) (3d), Mo(NAr)(CCMe2Ph)(Me2Pyr)(bipy) (4a), and Mo(NArT)(CCMe3)(Me2Pyr)(bipy) (ArT = 2-(2,4,6-i-Pr3C6H2)C6H4; 4g) showed structures with the normal bond lengths and angles.

The synthesis and full characterization, including Nuclear Magnetic Resonance (NMR) data ((1)H, (13)C{(1)H} and (119)Sn{(1)H}), for a series of Me3SnX (X = O-2,6-(t)Bu2C6H3 (), (Me3Sn)N(2,6-(i)Pr2C6H3) (), NH-2,4,6-(t)Bu3C6H2 (), N(SiMe3)2 (), NEt2, C5Me5 (), Cl, Br, I, and SnMe3) compounds in benzene-d6, toluene-d8, dichloromethane-d2, chloroform-d1, acetonitrile-d3, and tetrahydrofuran-d8 are reported. The X-ray crystal structures of Me3Sn(O-2,6-(t)Bu2C6H3) (), Me3Sn(O-2,6-(i)Pr2C6H3) (), and (Me3Sn)(NH-2,4,6-(t)Bu3C6H2) () are also presented. These compiled data complement existing literature data and ease the characterization of these compounds by routine NMR experiments.

In this paper we describe the syntheses of several new stereogenic-at-metal imido alkylidene complexes of molybdenum, Mo(NR)(CHR′)(X)(Y), many of which had to be prepared through selective nucleophilic displacement reactions in imido alkylidene complexes. H 3 (Ar, 6a), 2,6-Me 2 C 6 H 3 (Ar′, 6b), 2-iPrC 6 H 4 (Ar iPr , 6c), Ad (6d)), Mo(NR)(CHCMe 2 Ph)(OR F6 )[N(H)HMT] (7a (R = Ar′) and 7b (R = Ar iPr )), and Mo(NAd)(CHCMe 2 Ph)(OR F6 )(HMT) (8). X-ray structural studies were carried out on 1b, 2a−c, 3(PMe 3 ), 4, 5, 6d, 7b, and 8. Compound 1b is an octamer in which two η 1 -pyrrolides are trans to one another at each metal center and cyano groups bind from neighboring Mo centers trans to the alkylidene and imido ligands. ■ INTRODUCTIONRecent advances in olefin metathesis by molybdenum, 1 tungsten, 2 and ruthenium 3 alkylidene complexes have focused on initiators in which the metal is a stereogenic center. For example, the chemistry of high-oxidation-state molybdenum or tungsten complexes of the type M(NR)(CHR′)(OR″)(Pyr), where Pyr is a pyrrolide or a substituted pyrrolide (MAP complexes) were first prepared in 2007 4,5 in the process of demonstrating that a M(NR)(CHR′)(Pyr) 2 complex 6,7 could act as a precursor to a bisalkoxide, a biphenolate, or a binaphtholate imido alkylidene catalyst through addition of the monoalcohol or diol to it. Recent examples of selective metathesis applications by MAP catalysts that contain a sterically demanding HIPTO ligand (HIPTO − = hexaisopropylterphenoxide = O-2,6-(2,4,6-iPr 3 C 6 H 2 ) 2 C 6 H 3 -) or HMTO ligand (HMTO − = hexamethylterphenoxide = O-2,6-(mesityl) 2 C 6 H 3 -) include Z-selective metathesis homocoupling of terminal olefins, 8 Z-selective ringopening metathesis polymerization (ROMP) of 2,3-disubstituted norbornenes and norbornadienes, 9 Z-selective ring-opening/ cross-metathesis reactions, 10 ethenolysis reactions 11 (including Z-selective ethenolysis 12 ), and Z-selective cross-metathesis 1c or ring-closing metathesis. 2a Theoretical calculations by Eisenstein and co-workers 13 help explain why olefin metatheses by MAP species are relatively efficient. Isolation of 4-coordinate 14-electron methylidene species when the aryloxide is sterically demanding is consistent with the relatively long lived nature of MAP catalysts under some circumstances. 14 Syntheses of MAP species via the "protonolysis" route is proposed to involve binding of ROH to the metal through the oxygen atom before a proton migrates to the pyrrolide, probably to the α carbon atom first to yield an intermediate pyrrolenine complex. 15 Therefore, syntheses of MAP species via the protonolysis route strongly depend upon steric factors associated with the size of the pyrrolides (so far usually parent pyrrolide or a 2,5-dimethylpyrrolide), the imido, the alkylidene, and the added ROH. Another persistent synthetic problem is that intermediate MAP species can react with a another 1 equiv of alcohol to form a bisalkoxide. In short, in our experience, many potentially useful MAP species cannot be made i...

Monaryloxide pyrrolide (MAP) molybdenum imido alkylidene complexes of the type Mo(NAr X )(CHCMe 2 R)(Me 2 Pyr)(OR′) (Me 2 Pyr = 2,5dimethylpyrrolide) have been prepared in which NAr X is an ortho-substituted phenylimido group (X = Cl (NAr Cl ), CF 3 (NAr CF3 ), i-Pr (NAr iPr ), t-Bu (NAr tBu ), mesityl (NAr M ), or TRIP (TRIP = triisopropylphenyl; NAr T )) and OR′ = O-2,3,5,6-The object was to explore to what extent relatively "large" NAr M or NAr T ligands would alter the performance of MAP catalysts in reactions that have been proposed to depend upon the relative size of the imido and OR′ groups. Preliminary studies employing the ring-opening metathesis polymerization of 5,6-dicarbomethoxynorbornadiene as a measure of selectivity suggest that a single phenylimido ortho substituent, even in an NAr M or NAr T group, does not produce any unique behavior and that the outcome of the ROMP reaction correlates with the overall relative size of the imido and OR′ group. Single-crystal X-ray structures of six species that contain the new NAr M or NAr T groups are reported.