Structure and photoreactivity of stable zwitterionic group 6 metal allenyls (original) (raw)
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A new method for the preparation of N-stabilized allenylidene complexes of chromium and tungsten
Journal of Organometallic Chemistry, 2003
Displacement of tetrahydrofuran in [(CO) 5 M(THF)] (M 0/Cr, W) by the anion [C Å/C Ã/C(Ä/X)Y] ((X 0/O; NR; Y 0/NR ? 2 , Ph) followed by alkylation of the resulting metalate with [R ƒ 3 O]BF 4 (R ƒ0/Me, Et) offers a convenient and versatile route to p-donorsubstituted allenylidene complexes, [(CO) 5 M Ä/C Ä/C Ä/C(XR ƒ)Y]. Allenylidene complexes in which the terminal carbon atom of the allenylidene ligand constitutes part of a heterocycle are likewise accessible by this reaction sequence. Reaction of [(CO) 5 M(THF)] with Li[C Å/C Ã/C(Ä/NMe)Ph] (and subsequent protonation of the metalate afford [(CO) 5 M Ä/C Ä/C Ä/C(NMeH)Ph] in high yield. As indicated by the spectroscopic data of the compounds and the X-ray analyses of three representative examples, these allenylidene complexes are best described as hybrids of allenylidene and zwitterionic alkynyl complexes with delocalisation of the electron pair at nitrogen towards the metal center. Dimethylamine reacts with the amino(phenyl)allenylidene complex [(CO) 5 Cr Ä/C Ä/C Ä/ C(NMe 2)Ph] (7a) by addition of the amine across the C a Ä/C b bond to give selectively the E-alkenyl(amino)carbene complex [(CO) 5 Cr Ä/C(NMe 2) Ã/CH Ä/C(NMe 2)Ph] (12). In contrast, the reaction of dimethylamine with the amino(methoxy)allenylidene complex [(CO) 5 Cr Ä/C Ä/C Ä/C(NMe 2)OMe] (1a) proceeds by addition of the amine to the C g atom and subsequent elimination of methanol to give the substitution product [(CO) 5 Cr Ä/C Ä/C Ä/C(NMe 2) 2 ] (13). Triphenylphosphane neither adds to the C a nor the C g atom of 7a but upon irradiation displaces a CO ligand to form a cis-allenylidene(tetracarbonyl)phosphane complex 15.
An Entry to Mixed NHC-Fischer Carbene Complexes and Zwitterionic Group 6 Metal Alkenyls
Chemistry (Weinheim an der Bergstrasse, Germany), 2016
The addition of NHCs to α,β-unsaturated Cr(0) and W(0) (Fischer) carbene complexes is strongly dependent on the electrophilicity of the carbene carbon. Electrophilic alkoxy-carbene complexes quantitatively react with NHCs to yield stable zwitterionic (racemic) Cr(0) - and W(0) -alkenyls with total regio- and E-stereoselectivity. Less electrophilic aminocarbenes react with NHCs to promote the displacement of a CO ligand and yield "mixed" NHC/Fischer biscarbenes in a process that is unprecedented in group 6 metal-carbene chemistry. In fact, the compounds prepared, are some of the scarce examples of Fischer bisylidenes reported in the literature. The electrochemistry of the zwitterionic Cr(0) - and W(0) -alkenylcomplexes made, show that these compounds have a strong reductor character, which is demonstrated in their reactions towards [Ph3 C][PF6 ]. The oxidation processes lead to new types of cationic Fischer mono- and biscarbene complexes having a charged NHC fragment in the...
Inorganica Chimica Acta, 2009
Bis(ferrocenyl) substituted allenylidene complexes, [(CO) 5 M C C CFc 2 ] (1a c, Fc = (C 5 H 4 )Fe(C 5 H 5 ), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc 2 C O with Me 3 Si C CH, KF/MeOH, n BuLi, and [(CO) 5 M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO) 5 Cr C C C(Fc)R] (R = Ph, NMe 2 ), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HC CC(Fc)(Ph)OH with [(CO) 5 Cr(THF)] followed by desoxygenation with Cl 2 C O, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO) 5 Cr C(OR)CH C(NMe 2 )Fc], and (c) replacement of OMe in [(CO) 5 Cr C C C(OMe)NMe 2 ] by Fc. Complex 1a was also formed when the mono(ferrocenyl)alleny lidene complex [(CO) 5 Cr C C C(Fc)NMe 2 ] was treated first with Li[Fc] and the resulting adduct then with SiO 2 .
Journal of Organometallic Chemistry, 2006
Heterocyclic carbene complexes are accessible from p-donor-substituted allenylidene complexes, [(CO) 5 Cr@C@C@C(NMe 2)Ph] (1) and [(CO) 5 Cr@C@C@C(O-endo-Bornyl)OEt] (4), and various dinucleophiles by 1,2,3-diheterocyclization. The reaction of 1 with 1,2dimethylhydrazine gives the 1,2-dimethylpyrazolylidene complex [(CO) 5 Cr=C-C(H)=C(Ph)-NMe-NMe] (2) in high yield in addition to small amounts of the a,b-unsaturated carbene complex [(CO) 5 Cr@C(NMe 2)-C(H)@C(NMe 2)Ph] (3). The analogous reaction of 4 with 1,2-dimethylhydrazine affords the 1,2-dimethylpyrazolylidene complex [(CO) 5 Cr=C-C(H)=C(O-endo-Bornyl)-NMe-NMe] (5) and, via displacement of the C c-bound ethoxy substituent, the hydrazinoallenylidene complex [(CO) 5 Cr@C@C@C(O-endo-Bornyl){NMe-N(H)Me}] (6). Treatment of 6 with catalytic amounts of acids induces cyclization to 5. On addition of 1,1-dimethylhydrazine to 1 the zwitterionic pyrazolium-5-ylidene complex [(CO) 5 Cr-C=C(H)-C(Ph)=N-NMe 2 ] (7) is formed. The reaction of 1 with 1,2-diaminocyclohexane affords a octahydro-benzo[1,4]diazepinylidene complex (10) and, via intermolecular substitution, a binuclear bisallenylidene complex (11). Thiazepinylidene complexes (12-14), containing 7-membered N/S-heterocyclic carbene ligands, are formed highly selectively in the reaction of 1 with 2-aminoethanethiol or related cysteine derivatives by a substitution/cyclization sequence. The analogous reaction of 1 with homocysteine methylester yields a thiazocanylidene complex (15). All new heterocyclic carbene ligands are strong donors exhibiting r-donor/ p-acceptor ratios similar to those of the known imidazolylidene complexes. On photolysis of 2 and 12 in the presence of triphenylphosphine, the corresponding cis-carbene tetracarbonyl triphenylphosphine complexes (16 and 17) are formed. The solid state structure of complexes 2, 7, 14, 15, and 16 is established by X-ray structural analysis.
Organometallics, 2002
Reaction of the rhenium(I) allenylidene complex [Re{CdCdCPh 2 }(CO) 2 (triphos)]OTf (1; triphos ) MeC(CH 2 PPh 2 ) 3 , OTf ) -OSO 2 CF 3 ) with thiophenol, 2-thionaphthol, or allyl mercaptan gave selectively the R, -unsaturated thiocarbene complexes [Re{C(SR)CHdCPh 2 }-(CO) 2 (triphos)]OTf (R ) Ph (2), R-naphthyl (3), CH 2 CHdCH 2 (4)). A reversible reaction was observed for PhSH in DMSO at 80°C. Compounds 2 and 3 have been found to react with sodium alkoxides, yielding the kinetic thioallenyl products [Re{C(SR)dCdCPh 2 }(CO) 2 -(triphos)] (R ) Ph (6a), R-naphthyl (7a)). These equilibrated in room-temperature solution with the thermodynamic thioalkynyl products [Re{CtCC(SR)Ph 2 }(CO) 2 (triphos)] (R ) Ph (6b), R-naphthyl (7b)) to give stationary states (6a/6b, 40/60; 7a/7b, 20/80). Deprotonation of the thioallyl complex 4 gave the stable allenyl derivative [Re{C(SCH 2 CHdCH 2 )dCdCPh 2 }-(CO) 2 (triphos)] (8). Ammonia, aniline, and propargylamine each reacted with 1 to give the azoniabutadienyl compounds [Re{C(dNHR)CHdCPh 2 }(CO) 2 (triphos)]OTf (R ) H (9), Ph (10), CH 2 CtCH (11)) via N-H bond addition across the C R dC double bond. NMR spectroscopy showed the γ-alkynylammonium complex [Re{CtCCPh 2 (NH 3 )}(CO) 2 (triphos)]OTf (12) to be a transient intermediate along the reaction of 1 with ammonia. Treatment of 10 or 11 with sodium methoxide resulted in the selective deprotonation of the nitrogen atom to give the azabutadienyl compounds [Re{C(dNR)CHdCPh 2 }(CO) 2 (triphos)] (R ) Ph (13), CH 2 CtCH (14)). The molecular structure of the azoniabutadienyl complex 11 was determined by a single-crystal X-ray analysis. The geometry around the rhenium center conforms to a slightly distorted octahedron, with the polyphosphine sitting on a face of the coordination polyhedron. In keeping with the azoniabutadienyl structure, the Re-C R bond length is 2.151(7) Å, and the C R -N distance is 1.300(9) Å.
Inorganica Chimica Acta, 2006
The reaction of [(g 7 -C 7 H 7 )Zr(g 5 -C 5 H 5 )] with two Lewis bases, tetramethylimidazolin-2-ylidene and PMe 3 , is reported and their stability probed via spectroscopic and theoretical methods. The strongly r-basic N-heterocyclic carbene forms a stable adduct which has been structurally characterised, whilst the PMe 3 ligand coordinates weakly to the metal centre. Variable temperature 31 P NMR spectroscopy has been used to determine the activation energy for this process (DG à = 40.5 ± 1.9 kJ mol À1 ). DFT calculations have been performed on both complexes and the structures discussed. In addition, the enthalpies for the formation of these compounds have been calculated [DH 0 (Zr-IMe) = À56.3 kJ mol À1 ; DH 0 (Zr-PMe 3 ) = À2.3 kJ mol À1 ] and show that the N-heterocyclic carbene forms a thermodynamically much more stable adduct than that with PMe 3 .
Journal of Coordination Chemistry, 2006
Five new complexes, [M(CO) 5 (apmsh)] [M = Cr; (1), Mo; (2), W; (3)], [Re(CO) 4 Br(apmsh)] (4) and [Mn(CO) 3 (apmsh)] (5) have been synthesized by the photochemical reaction of metal carbonyls [M(CO) 6 ] (M ¼ Cr, Mo and W), [Re(CO) 5 Br], and [Mn(CO) 3 Cp] with 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh). The complexes have been characterized by elemental analysis, mass spectrometry, f.t.-i.r. and 1 H spectroscopy. Spectroscopic studies show that apmsh behaves as a monodentate ligand coordinating via the imine N donor atom in [M(CO) 5 (apmsh)] (1-4) and as a tridentate ligand in (5).