Synthesis and Structural Investigations of manganese carbene complexes

The study involves the synthesis and structural characterization of manganese carbene complexes. The synthesis of dimanganese monocarbene complexes [Mn2(CO)9{C(OEt)(heteroaryl)}] was done via the classical Fischer method, and a range of complexes containing heteroaromatic substituents, e.g. 2,2'-bithiophene, thiophene, furan and N-methyl pyrrole, was isolated. These complexes displayed a novel configuration with the carbene ligand in the axial position, in contrast to the equatorial position found for the analogous rhenium compound and other dimanganese complexes known from the literature. The possibility of manipulating the position of the carbene ligand in the binuclear complexes was investigated by a nucleophilic substitution of the ethoxy substituent with an amine substituent. Only aminolysis with small, primary amines such as ammonia and propylamine, proved successful. The propylaminocarbene ligands retained their axial configuration, but a conversion to the more thermodynamically stable equatorially substituted carbene ligands was observed for the complexes [Mn2(CO)9{C(NH2)(heteroaryl)}], while mixtures of the equatorial and axial isomers were observed in solution. Structural X-ray analysis proved that although the equatorial position is more electronically favourable, steric hindrance by the second manganese pentacarbonyl moiety prevented ethoxy- and propylamino-substituted carbene ligands to adopt this configuration. A kinetic study of the aminolysis reaction was done in an effort to elucidate the reaction mechanism and to explain the axial-equatorial conversion. Due to the competing decomposition reaction of the product and reagent complexes with that of the substitution reaction, no information about reaction intermediates could be obtained. The target mononuclear complexes [Mn(CO)4{C(OEt)(heteroaryl)}X] (X = Br, I) was obtained by cleavage of the metal-metal bond of the binuclear precursor complexes. Cleaving of the Mn-Mn bond was done oxidatively by halogens, without affecting the carbene ligand. The product complexes have an assembly resembling that of the Grubbs ruthenium metathesis catalyst. Interestingly, the cleaved complexes were found to have a cis configuration of the carbene and halide ligand. Copyright 2006, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bezuidenhout, DI 2006, Synthesis and Structural Investigations of manganese carbene complexes, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd Dissertation (MSc)--University of Pretoria, 2007.Chemistryunrestricte

Multimetal complexes of Fischer carbenes

Fischer carbene complexes of the Group VI transition metals (Cr, Mo and W) containing at least two or three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesized and studied both in solution and in the solid state. For the complexes of the type [M(CO)5{C(OR)R’}], the substituents chosen included (hetero)aromatic (benzene or thiophene) rings π-bonded to a chromium tricarbonyl fragment or ferrocene as the R’-substituent, while the OR-substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1 (M = Cr, R = Et, R’ = Fc), 2 (M = W, R = Et, R’ = Fc), 5 (M = Cr, R = TiCp2Cl, R’ = Fc), 6 (M = W, R = TiCp2Cl, R’ = Fc), 7 (M = Mo, R = TiCp2Cl, R’ = Fc), 12 (M = Cr, R = TiCp2Cl, R’ = 2-thienyl) and 13 (M = Cr, R = TiCp2Cl, R’ = [Cr(CO) 3 (η 6-phenyl)]). Direct lithiation of the ferrocene with n-BuLi/TMEDA at elevated temperatures, followed by the Fischer method of carbene preparation, also resulted, in most cases, in the formation of the novel biscarbene complexes with bridging ferrocen- 1,1’-diyl carbene ligands [μ-Fe{C5H4C(OEt)M(CO) sub>5}2] (3: M = Cr, 4: M = W) or the unusual bimetallacyclic bridged biscarbene complexes [{μ-TiCp2O2-O,O’}{μ- Fe(C5H4)2-C,C’}{CM(CO) 5}2] (8: M = Cr, 9: M = W, 10: M = Mo). It was attempted to prepare the mixed heteronuclear biscarbene complex 11 [W(CO) 5C{μ-TiCp2O2- O,O’}{μ-Fe(C5H4)2-C,C’}CCr(CO) 5], however the complex could not be fully characterized. The investigation was expanded to include Group VII transition metals Mn and Re, and using the same methodology, the manganese complexes isolated included [MnCp(CO2{C(OR)Fc}] (22: R = Et, 24: R = TiCp2Cl), 23 [μ- Fe{C5H4C(OEt)MnCp(CO) 2}2] and 25 [{μ-TiCp2O2-O,O’}{μ- Fe(C5H4)2- C,C’}[CMnCp(CO) 2}2]. The different reactivity of the binary dirhenium decacarbonyl precursor complex, compared to that of the Group VI complexes, resulted in the formation of a range of complexes. The target compounds [Re2 (CO) 9{C(OR)Fc}] (26: R = Et, 31: R = TiCp2Cl), 27 [μ-Fe{C5H4C(OEt)Re2 (CO) 9}2] and 33 [{μ- TiCp2O2-O,O’}{μ-Fe(C5H4)2-C,C’}[CRe2 (CO) 9}2] were isolated displaying a variety of different geometric isomers. In addition, acyl (30) and aldehyde (32) decomposition products, as well as hydrido (29), and hydrido acyl hydroxycarbene (34) complexes and the unique dichloro-bridged biscarbene complex (28) were also characterized. Most of these complexes displayed Re-Re bond breaking, and two probable mechanisms, either radical or ionic, were proposed involving either hydrogen transfer or protonation followed by hydrolysis. Finally, the structural features and their relevance to bonding in the carbene cluster compounds of the Group VI transition metals were investigated as they represent indicators of possible reactivity sites in multimetal carbene assemblies. The possibility of using DFT calculations to quantify the effect of metal-containing substituents on the carbene ligands was tested and correlated with experimental parameters by employing methods such as vibrational spectroscopy, molecular orbital analysis, and cyclic voltammetry. The best results were obtained from the cyclic voltammetric studies, where the localized metal centre’s oxidation potential correlated to both the calculated HOMO energy, and the effect of both the heteroatom substituent and the (hetero)arene substituent, as well as different combinations of the above.Thesis (PhD)--University of Pretoria, 2010.Chemistryunrestricte

Ruthenium(II) pincer complexes featuring an anionic CNC bis(1,2,3-triazol-5-ylidene)carbazolide ligand coordinated in a meridional fashion

Please read abstract in the article.GGB thanks the MINECO for a postdoctoral grant (IJCI-2015-23407); EP gratefully acknowledges financial support from MINECO of Spain (CTQ2014-51999-P) and the Universitat Jaume I (P11B2014-02); DIB and GK gratefully acknowledge the National Research Foundation, South Africa (NRF 10552, 105740 and 92521), and Sasol Technology R&D Pty. Ltd., South Africa.http://www.elsevier.com/locate/poly2019-03-15hj2017Chemistr

Recent advances in the field of multicarbene and multimetal carbene complexes of the Fischer-type

This review article covers the development of Fischer carbene complexes since the year 2000, with specific focus on carbene complexes bearing metal-containing fragments as substituents, as well as multicarbene systems. The role of the metal-containing substituents on the character and reactivity of such complexes are discussed. In addition, larger systems containing more than one carbene ligand are also covered (rodlike biscarbenes, chelates, macrosystems, etc.) in terms of the synthesis, reactivity and structural aspects.http://www.elsevier.com/locate/ccrhb201

1,3-Bis(2,4,6-trimethylphenyl)-3H imidazol-1-ium tetraoxidorhenate(VII)

The title compound, (C21H25N2)[ReO4], was formed as the unexpected product in an attempted synthesis of a rhenium(I)–N-heterocyclic carbene (NHC) complex. The compound has crystallographic mirror symmetry with both the cation and the tetrahedral anion located across a mirror plane. The cation and anion are linked by a C—H O hydrogen bond.The University of Pretoria and the National Research Foundationhttp://journals.iucr.org/e/journalhomepage.htmlnf201

Synthesis and structure of annulated dithieno[2,3- b ;3 ʹ,2 ʹ- d ]thienyl- and ring-opened 3,3 ʹ-bithienyl Fischer carbene complexes

Please read abstract in the article.Appendix A. Supplementary data.Appendix B. checkCIF/PLATON reportResearch data for this article: Cambridge Crystallographic Data Center. Crystallographic data: CCDC 2009041: Experimental Crystal Structure Determination (https://www.ccdc.cam.ac.uk/structures/search?id=doi:10.5517/ccdc.csd.cc25fksz&sid=DataCite)CCDC 2009042: Experimental Crystal Structure Determination (https://www.ccdc.cam.ac.uk/structures/search?id=doi:10.5517/ccdc.csd.cc25fkt0&sid=DataCite)CCDC 2009043: Experimental Crystal Structure Determination (https://www.ccdc.cam.ac.uk/structures/search?id=doi:10.5517/ccdc.csd.cc25fkv1&sid=DataCite)CCDC 2009044: Experimental Crystal Structure Determination (https://www.ccdc.cam.ac.uk/structures/search?id=doi:10.5517/ccdc.csd.cc25fkw2&sid=DataCite)CCDC 2009045: Experimental Crystal Structure Determination (https://www.ccdc.cam.ac.uk/structures/search?id=doi:10.5517/ccdc.csd.cc25fkx3&sid=DataCite)CCDC 2009046: Experimental Crystal Structure Determination (https://www.ccdc.cam.ac.uk/structures/search?id=doi:10.5517/ccdc.csd.cc25fky4&sid=DataCite)CCDC 2009047: Experimental Crystal Structure Determination (https://www.ccdc.cam.ac.uk/structures/search?id=doi:10.5517/ccdc.csd.cc25fkz5&sid=DataCite)The National Research Foundation, South Africa and Sasol Technology R&D Pty. Ltd. (South Africa).http://www.elsevier.com/locate/jorganchemam2021Chemistr

(Spectro)electrochemical investigations on (ferrocenyl)thiophenes modified by tungsten Fischer carbenes

Please abstract in the article.National Research Foundation, South Africa and Fonds der Chemischen Industrie and Chemifonds Fellowships.http://www.elsevier.com/locate/jorganchem2015-12-31hb201

Synthesis and properties of mono- and dimetal Fischer multicarbene complexes derived from thiophene and thieno[2,3-b]thiophene

Access to multicarbene complexes of a fused thienothiophene substrate was obtained by the use of the tetrabrominated thieno[2,3-b]thiophene precursor in a lithium–bromide exchange reaction, followed by nucleophilic attack on metal hexacarbonyls (M = Cr, W). Subsequent alkylation afforded unique triscarbene complexes [M(CO)4{{C(OEt)}2C6H1S2C(OEt)}M(CO)5] (M = Cr 12, W 13) featuring three non-equivalent carbene ligands on a single thiophene linker, as well as the bischelated tetracarbene complexes [M(CO)4{{C(OEt)}2C6S2{C(OEt)}2}M(CO)4] (M = Cr 14, W 15). The triscarbene complexes 12 and 13 are the first examples of multi-alkoxycarbene complexes featuring three non-equivalent carbene ligands. The reaction also afforded the chelated mononuclear biscarbene complexes [M(CO)4{C(OEt)}2C6H2S2] (M = Cr 10, W 11) in low yields. Similarly, employing tetrabromothiophene as precursor yielded the mononuclear chelate biscarbene complexes [M(CO)4{C(OEt)}2C4H2S] (M = Cr 6, W 7) and the dinuclear tetracarbene complexes [M(CO)4{{C(OEt)}2C4S{C(OEt)}2}M(CO)4] (M = Cr 8, W 9). Modification of the classic Fischer carbene synthetic methodology to a process of stepwise additions of lithiating agent and metal carbonyls to thieno[2,3-b]thiophene, facilitates the formation of the mixed metal biscarbene complex [W(CO)5C(OEt){C6H2S2}C(OEt)Cr(CO)5] 5, as analogue of the homonuclear biscarbene complexes [M(CO)5C(OEt){C6H2S2}C(OEt)M(CO)5], (M = Cr 3, W 4). The monocarbene complexes [M(CO)5{C(OEt)- C6H3S2}], (M = Cr 1, W 2) were also obtained in high yields, and the molecular structures of the tungsten complexes, with the exception of 9 and 11, were confirmed by single crystal X-ray diffraction studies.The National Research Foundation (NRF) of South Africa with grants to SL (no. 73679 and 77079) and DIB (no. 87890 and 92521).http://www.rsc.org/dalton2016-10-13am201

Electrochemical and computational study of tungsten(0) ferrocene complexes: observation of the mono-oxidized tungsten(0) ferrocenium species and intramolecular electronic interactions

The series [(CO)5W=C(XR)Fc], 1 (XR = OEt) and 3 (XR = NHBu) as well as [(CO)5W=C(XR)-Fc'-(XR)C=W(CO)5], 2 (XR = OEt) and 4 (XR = NHBu) of mono- and biscarbene tungsten(0) complexes with Fc = FeII(C5H5)(C5H4) for monosubstituted derivatives and Fc¢ = FeII(C5H4)2 for disubstituted derivatives were synthesized and characterized spectroscopically. The oxidized ferrocenium complex [1+]•PF6 was also synthesized and characterized. Electrochemical and computational studies were mutually consistent in confirming the sequence of redox events for the carbene derivatives 1 - 4 as first a carbene double bond reduction to a radical anion, -W-C•, at peak cathodic potentials smaller than -2 V, then a ferrocenyl group oxidation in the range 0.206 < Eo' < 0.540 V and finally an electrochemically irreversible three-electron W(0) oxidation at Epa > 0.540 V vs. FcH/FcH+ in CH2Cl2 / [(nBu4)N][PF6]. This contrasts the sequence of oxidation events in ferrocenylcarbene complexes of chromium where Cr(0) is first oxidised in a one electron transfer process, then the ferrocenyl group, and finally formation of a Cr(II) species. The unpaired electron of the reductively formed radical anion is mainly located on the carbene carbon atom. Electronic interactions between two carbene double bonds (for biscarbenes 2 and 4) as well as between two W centers (for 4) were evident. Differences in redox potentials between the “a” and “b” components of the threeelectron W oxidation of 4 in CH2Cl2 or CH3CN / [(nBu4)N][PF6] are DEo' = Epa W(0) oxd 1b – Epa W(0) oxd 1a = ca. 51 and 337 mV respectively. Tungsten oxidation was restricted to a W0/II couple in CH2Cl2 / [(nBu4)N][B(C6F5)4]. From the computational results, the short-lived W(II) species were observed to be stabilized by agostic CH···W interactions.National Research Foundation, South Africa, (DIB, Grant number 76226; JCS, Grant number 81829), and by the Spanish MICINN and CAM (IF, Grants CTQ2010-20714-CO2-01/BQU, Consolider-Ingenio 2010, CSD2007-00006, S2009/PPQ-1634).http://pubs.acs.org/journal/orgnd7hb201

Rhenium ethoxy- and hydroxycarbene complexes with thiophene substituents

Please read abstract in article.This work was supported financially by the University of Pretoria and by the National Research Foundation (NRF) of South Africa under Grant number: 73679 (SL).http://www.rsc.org/dalto