Synthese von benzylidenverbrückten Bis(pentacarbonylwolfram)‐Komplexen durch Thermolyse terminaler Benzylidenpentacarbonylwolfram‐Komplexe

Abstract

Bei der Thermolyse der terminalen Benzylidenpentacarbonylwolfram-Komplexe (CO),W-[C(H)C&R-p] (R =H -3a-c and trans-3a-c). The product ratio cis-3/trans-3 depends on the type of solvent. The reaction rate decreases with increasing donor ability of the substituent R. The reaction of l c with (C0)5W(CH2C12) also yields 2c. The structure of complex 2a is confirmed by X-ray analysis. The reactivity of the terminal complexes 1 is determined by the extremely high electrophilicity of the benzylidene carbon.In contrast, 2a reacts (a) with Me3N+ -0-via oxidative elimination of CO in the form of COz and (b) with PPh3 via primary CO-dissoziation to give carbonyl(ph0sphane) complexes. 2a is not protonated by trifluoroacetic acid.Bei einer Reihe von katalytischen Prozessen wie z. B. Cyclopropanierung, Olefinmetathese und Alkinpolymerisation werden fjbergangsmetall-Komplexe mit terminal gebundenen bzw. verbruckenden CR'R2-Liganden als reaktive Zwischenstufen diskutiert'). Der Wechselbeziehung zwischen beiden Bindungsarten sowie dem Vergleich der Reaktivitat von Komplexen mit dern gleichen CR1R2-Liganden 0 VCH Verlagsgesellschaft mbH, D

Reductive Trapping of [(OC)5W–W(CO)5]2− in a Mixed‐Valent SmII/III Calix[4]pyrrolide Sandwich

“…More frequently observed are positively charged W 2 (CO) 10 moieties in which negatively charged bridging coligands enable a1 8-VE configuration to be achieved, for example,[ W 2 (CO) 10 (m-CHPh)]. [13] Both tungsten atoms of 1 are six-coordinate with the two W(CO) 4 planes staggered, and the WÀWb ond length (3.1107 (6) [14] and seven-coordinate [Cp*W(CO) 3 ] 2 (3.288 (1) ). [15] Theb ridging isocarbonyl C À Ob ond (1.201(10) )b etween Sm and Watoms is longer than the average of the terminal carbonyl C À Obonds (1.14 ).…”

Unexpected Zwitterionic Allenyls from Silylenes and a Fischer Alkynylcarbene: A Remarkable Silylene‐Promoted Rearrangement

“…[1a, 2b] In this context,w e have recently achieved the first insertion of ac arbenef ragment into an NÀSi bond by treatinga na midinatosilylenew ith at ungsten Fischer methyl(ethoxy)carbene complex at room temperature (Scheme 1). [7] In contrast, similar reactions using phosphanes [8] or NHCs [9] afford carbonyl-and/orc arbene-sub-stituted products.N oteworthy,a lthough group 6m etal Fischer carbene complexes are frequently used as precursors of carbene synthons, [10,11] the transfero ft he carbene fragment requires catalysts [11h-m] or harshr eaction conditions (> 120 8C). [11a-g] We now report that, studying reactions of amidinatosilylenes with group 6m etal Fischer alkynyl(ethoxy)carbenec omplexes, we have unexpectedly obtained zwitterionic s-allenyl complexesi nw hich the originalc arbene Ca tom forms part of both the allene fragment and of aS i-C-N-C-N five-membered ring.…”

Two Types of σ‐Allenyl Complexes from Reactions of Silylenes and Germylenes with Chromium Fischer Alkynyl(alkoxy)carbenes

“…It is noteworthy that the metal atom (Cr1) is now attached to the same Ca tom as the ferrocenyl group (C25, originally the C g atom of 2 Fc )a nd that the originalC carbene atom of 2 Fc (C27, C a )h as ended inserted into aG e ÀNb ond of the originalg ermylene 1 Ge-Tmsm .A dditionally,t he ethoxy group has been transferred from C a to the germanium atom. Given that the moleculeh as two stereogenicg roups (the germanium (2), C25ÀC26 1.303 (3), C25ÀO1 1.398 (2), C26ÀC27 1.336 (3), C27ÀC281.500 (2), Si1ÀC27 1.846 (2), Si1ÀC16 1.869 (2),S i1ÀN1 1.795 (1), Si1À N2 1.818 (2);C25-C26-C27 172.9 (2). (8), C25ÀC261.30 (1), C25ÀO1 1.408 (8), C26ÀC27 1.319 (9), C27ÀC281.508 (9), Ge1ÀC271.909 (7),G e1ÀC16 1.904 (7), Ge1ÀN1 1.929 (6), Ge1ÀN2 1.935 (5); C25-C26-C27 174.2 (8). atom and the allene fragment), it is also notablet hat only one diastereoisomer was formed, the one that has the ethoxya nd ferrocenyl groups at the same side of the Ge-C-N-C-N fivemembered ring.…”

“…Given the strongb asicity of N-heterocyclic carbenes (NHCs) [1] and the high electrophilicity of Group 6m etal Fischer carbenes of the type [M{C(OEt)R'}(CO) 5 ], [2] it was surprising that combinations of these two reagents did not involve the nucleophilic attack of the NHC to the Fischer C carbene atom;i nstead, these reactions afforded carbene substitution (M = Cr;R ' = alkyl or aryl) [3] or conjugate addition (M = Cr,W ;R ' = alkenyl [4] or alkynyl [5] )p roducts (Scheme 1).…”

“…[3][4][5] heating, the reactions involving chromium Fischer carbenes end in [Cr{Ge(tBu 2 bzm)tBu}(CO) 5 ]( Scheme 2). [13] In addition, from reactions of the amidinatosilylenesS i(t-Bu 2 bzm)R 1 (R 1 = mesityl ( 2,4, ) 3 C 6 H 2 ,M es), CH 2 SiMe 3 (Tmsm)) with [W{C(OEt)C 2 Ph}(CO) 5 ], we succeeded in synthesizing unprecedented zwitterionic metal-allenyl complexes in which the original carbene C a atom forms part of both the allene fragment and of aS i-C-N-C-Nf ive-membered ring (Scheme 3). [14] We now reportareactivity study that involves reactions at varioust emperatures of two amidinatosilylenes and three amidinatogermylenes with two chromiumF ischer alkynyl(ethoxy)carbene complexes.T his thorough study,t ogether with the tungstenr esultsshown in Scheme 3, [14] provides an ample panorama of the reactivity of amidinato-HTsw ith Group 6m etal Fischeralkynyl(ethoxy)carbene complexes, showing that the reactions may follow three different pathways (attack of the HT to the C a ,C g ,o rMatoms of the metal complex), the outcome of ap articularr eactiond epending upon the reaction temperature, the Group 6m etal atom (Cr or W), the tetrel atom (Si or Ge), and the volumes of both the amidinato-HTand the alkynyl terminal group.…”