Li[Cp2Zr(CCPh)(η2∶1,2PhC2CCPh)]: an anionic zirconium(ii) intermediate for carbon–carbon coupling

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  Li[Cp2Zr(CCPh)(η2∶1,2PhC2CCPh)]: an anionic zirconium(ii) intermediate for carbon–carbon coupling
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  Li[Cp 2 Zr(C · CPh)( h 2 + 1,2-PhC 2 C · CPh)]: an anionic zirconium( II ) intermediatefor carbon–carbon coupling Robert Choukroun,* Jianshe Zhao, Christian Lorber, Patrick Cassoux and Bruno Donnadieu  Equipe Pr´ ecurseurs Mol´ eculaires et Mat´ eriaux, Laboratoire de Chimie de Coordination du CNRS, 205 Route de  Narbonne, 31077, Toulouse Cedex, France. E-mail: choukrou@lcc-toulouse.fr  Received (in Basel, Switzerland) 5th June 2000, Accepted 5th July 2000 Published on the Web 24th July 2000 The unexpected anionic Zr II complex[Cp 2 Zr(C · CPh)( h 2 + 1,2-PhC 2 C · CPh)] 2 was isolated fromLiC · CPh and Cp 2 ZrCl 2 in THF, giving clear evidence for aCC coupling between two alkynyl moieties, one of thembeing h 2 -bonded to the zirconium atom. New prospects towards non linear optical (NLO) materials haveinduced, in recent years, a resurgence of interest in thechemistry of acetylenic transition metals complexes. 1 Numer-ous studies have focused on the CC coupling of the acetylenicmoieties, which underlies the synthesis of the building block of the poly-ynes. 2 We have been interested in the reaction of vanadocene with poly-ynes. 3 An unexpected heterodimetalliccomplex Cp 2 V( m + h 2 + h 4 -PhC · CC · CPh))ZrCp 2 , containing abutadiene framework with two internal planar tetracoordinatecarbons was isolated from Cp 2 V and Cp A 2 Zr(C · CPh) 2 (Cp A =C 5 H 5 , C 5 H 4 Me, C 5 H 4 Bu t , C 5 H 4 SiMe 3 ). 4,5 The chemistry of these bis(alkynyl)metallocene precursors has previously beendetailed 6–8 and their synthesis, generally in diethyl ethersolvent, well described. 6 On the other hand, a CC bond formingreaction was reported by Negishi et al. 9 as resulting from thereaction of Cp 2 ZrCl 2 with 3 equiv. of LiC · CPh in THFfollowed by hydrolysis affording the isomerically pure (  Z  )-1,4-diphenylbut-1-ene-3-yne. In this process, Li[Cp 2 Zr-(C · CPh) 3 ] was postulated as an intermediate species. 9 Theauthors underline the necessity of the third equiv. of LiC · CPhto Cp 2 Zr(C · CPh) 2 to produce the CC coupling. More recently,the [Zr(C · CR) 3 ] 2 anion moiety was suggested as being anintermediate species in the trimerization of tert  -butyl acetyleneto 1,3,6-tri( tert  -butyl)fulvene. 10 We report here the X-raystructure of the intermediate anion speciesLi[CpZr(C · CPh)( h 2 + 1,2-PhC 2 C · CPh)] and some aspects of itsformation mechanism.When the reaction of Cp 2 ZrCl 2 with 2 equiv. of LiC · CPh iscarried out in THF, followed by slow diffusion of pentane, theunexpected Zr II lithium salt species Li[Cp 2 Zr(C · CPh)( h 2 + 1,2-PhC 2 C · CPh)] 1 ,† was obtained as a red crystalline complex andfully characterized by an X-ray structure determination (Fig.1).‡ The main feature of this structure gives clear evidence fora CC coupling between two alkynyl moieties, one of them being h 2 -bonded to the zirconium atom. A titanium complex related to 1 , namely (C 5 Me 5 ) 2 Ti( h 2 + 1,2-RC 2 C · CR)] was also recentlyisolated by Rosenthal et al. by Mg reduction of (C 5 Me 5 ) 2 TiCl 2 in the presence of Me 3 SiC 4 SiMe 3 . 11 a Depending on the ratio of the reactants, this reaction also affords either the tweezer Ti III complex [(C 5 Me 5 ) 2 Ti( h 1 -C · CSiMe 3 ) 2 ][Mg(THF)Cl)] (A) or[(C 5 Me 5 ) 2 Ti(( h 3 -Me 3 SiC 3 N C(C · CSiMe 3 )SiMe 3 ] 11 b (B). Thetweezer Ti III complex (A) could be described as an intermediatefor the formation of complex (B).Different crossing reactions were monitored by 1 H NMR togain an understanding of the formation of 1 .§ When the reactionof Cp 2 ZrCl 2 and 2 equiv. of LiC · CPh is carried out in THF andin the absence on sunlight, Cp 2 Zr(C · CPh) 2 2 was obtained asthe sole product and can be kept unchanged at least one week inthe dark, whereas in presence of daylight only 1 is formed. 12 Starting from 2 and the solid lithium salt LiC · CPh in THF-d 8 ,complete consumption of the Li salt gives 1 nearly immediatelyand quantitatively in absence or in presence of daylight. Wechecked that in the absence of daylight no reaction occurs inC 6 D 6 between 2 and LiC · CPh (1 + 1) whereas still in the absenceof daylight the addition of THF-d 8 in the NMR tube, whichdissolves the lithium salt, immediately generates 1 .Complementary hydrolysis experiments on complex 1 con-taining the preformed CC coupling were performed to ensurethat the 1,4-diphenylbut-1-en-3-yne is also formed in this case.In presence of HCl and at room temperature, hydrolysis of 1 leads to the formation of  E  and  Z  isomers of the enynePhCH N CHC · CPh with a high selectivity when the reaction iscarried out in toluene (toluene:  Z  +  E  = 98 + 2; THF:  Z  +  E  =30 + 70).¶ Adding LiC · CBu t to 2 followed by HCl hydrolysisgives  Z  enynes, namely PhCH N CHC · CBu t , PhC · CCH N CHBu t and PhCHCHC · CPh (roughly 30, 15, 55% respectively,characterized by GC/MS and 1 H NMR). ∑ This result suggeststhat the first step of the reaction is the formation of the Fig. 1 Molecular structure of anionic [ 1 ] 2 with selected bond distances (Å)and angles (°), hydrogen atoms omitted. Zr–C(11) 2.206(2), Zr–(C12)2.342(1), Zr–C(15) 2.314(2), C(11)–C(12) 1.335(2), C(12)–C(13) 1.412(2),C(13)–C(14) 1.208(2), C(15)–C(16) 1.223(2), Zr–Cp 2.252(av.); Zr–C(11)–C(111) 147.8(1), Zr–C(15)–C(16) 171.9(1), Zr–C(12)–C(13)127.9(1), C(12)–C(13)–C(14) 177.5(2), C(11)–Zr–C(12) 33.97(6), C(12)–Zr–C(15) 88.60(5), C(11)–Zr–C(15) 122.53(5), Zr–C(15)–C(16) 171.9(1),C(15)–C(16)–C(166) 176.3(2), Cp–Zr–Cp 129.57(av.) [Cp are the centroidsof the C 5 H 5 rings C(1)–C(5), C(6)–C(10)]. This journal is © The Royal Society of Chemistry 2000 DOI: 10.1039/b004478o Chem. Commun. , 2000, 1511–1512 1511  Li[Cp 2 Zr(C · CPh) 2 (C · CBu t )] intermediate which could givethree possible species such as Li[Cp 2 Zr(C · CPh)( h 2 + 1,2-PhC 2 C · CBu t )], Li[Cp 2 Zr(C · CPh)( h 2 + 1,2-Bu t C 2 C · CPh] andLi[Cp 2 Zr(C · CBu t )( h 2 + 1,2-PhC 2 C · CPh)], the formation of thelatter being favoured by the presence of the less steric R = Phgroup on the h 2 chain.**The CC coupling between two alkynyl moieties fromCp A 2 Zr(C · CR) 2 (Cp A = C 5 H 5 , R = Bu t ; Cp A = C 5 Me 5 , R = Ph,SiMe 3 ) has already been demonstrated by Rosenthal et al. 11,13,14 This reaction occurs under h n  irradiation or sunlightto give the zirconacyclocumulene complex Cp A 2 Zr( h 4 + 1,2,3,4-RC N C N C N CR). ††  Thus (C 5 H 5 ) 2 Zr( h 4 + 1,2,3,4-PhC N C N C N CPh) 3 should be an excellent candidate for explaining the formationof 1 . Starting from 3 , generated by h n  daylight in THF-d 8 from 2 , 12 addition of one equiv. of LiC · CPh gives 1 . This experimentis indicative of an equilibrium between the zirconacyclocumu-lene and a ( h 2 + 1,2-PhC 2 C · CPh) containing species (Scheme 1)as already mentioned by Rosenthal et al. 13 Nevertheless theformation of the zirconacumulene species must be catalysedeither by daylight, or by the B(C 6 F 5 ) 3 borane, 15 or by the Cp 2 Vvanadocene for at least one day. By contrast, the formation of the ( h 2 + 1,2-PhC 2 C · CPh) moiety in 1 is immediate in THFwhen adding the third LiC · CPh equiv. to the bis(alkynyl)zirco-nocene complex. No catalytic reaction from 2 to 3 withLiC · CPh as catalyst was observed by 1 H NMR.At this stage we are not in a position to prove the involvementof LiC · CPh in a photoassisted reaction with 2 leading to 1 .However, it is noteworthy that when the reaction is carried outin the dark, it yields only 2 . Our results clearly suggest that thealkynyl coupling reaction is induced by a third alkynyl ligand via the formation of the unstable ‘ ate ’  intermediate Zr IV speciesLi[Cp 2 Zr(C · CPh) 3 ], or an assumed tweezer Zr species[Cp 2 Zr(C · CPh) 2 ][Li(C · CPh)], which may subsequently re-arrange to 1 . 16 Notes and references † Spectroscopic data for C 42 H 41 LiO 2 Zr 1 :  M  = 675.9, Calc: C, 74.55; H,6.06. Found: C, 74.72; H, 5.86%; (40% yield based on 2 equiv. LiC · CPh;75% yield when the reaction is performed with 3 equiv. LiC · CPh). IR(Nujol): n  (C · C) 2063, 2110 cm 2 1 ; 1 H NMR (C 6 D 6 , d   /ppm) 8.26 (pseudotriplet, 2H, o -Ph from the h 2 -PhC 2 -bonded to the zirconium atom), 7.54 – 6.9(m, 13H, Ph), 5.78 (s, 10H, Cp), 3.36, 0.95 (m, 16H, THF). A 1 H NMR VTPof the complex from 2 80 to +80 ° C does not show any change in thesolution structure. Assignement of the 13 C NMR spectrum of 1 in THF-d 8 ( d   /ppm,  J  (Hz)) could be tentatively done with a JMOD and 2Dheteronuclear correlation technique (inverse HMQC (LR), gradient se-lected). Li[Cp 2 Zr(C a · C b Ph)( h 2 -PhC a · C b -C c · C d Ph)], 1 : 205.9 (s, 3  J  CH = 4Hz, C b ), 134.9, 130.4, (s, C a  /C a ), 97.6 (s, C c ), 126.4/107.4 (t, 3  J  CH = 4 – 5Hz, C b  /C d ), 142.5, 127.9, 128.3 (t, 2  J  = 7 – 8 Hz, C ipso ), 130.8, 129.8, 129.0,128.4, 128.2, 128.0, 126.1, 126.0, 125.8 (d, 1  J  CH = 158 – 162 Hz, Ph), 105.0(d, 1  J  CH = 171 Hz, Cp). ‡ Crystallographic data for 1 : C 34 H 25 LiZr · 2THF  M  = 675.95, monoclinic,space group P 2 1  /  c , a = 14.986(2), b = 10.4594(8), c = 22.028(2) Å , b  =102.07(1) ° , V  = 3376(1) Å 3 ,  D = 1.33 g cm 2 3 , m  = 3.61 cm 2 1 ,  R (  R w) =0.0272 (0.0722) for 4701 unique data and 415 parameters, G.O.F. = 1.04.Data collection were performed at ca. 160 K on a IPDS STOEdiffractometer using graphite monochromatized Mo-K a radiation. Thestructure was solved by direct methods and subsequent difference Fouriermaps. CCDC 182/1708. See htpp://www.rsc.org/suppdata/cc/b0/b004478o/ for crystallographic files in .cif format. § A suspension of Cp 2 ZrCl 2 (0.900 g, 3.08 mmol) was treated with 2 equiv.solid LiC · CPh (0.665 g, 6.16 mmol) in benzene for 4 h and species such asCp 2 ZrCl 2 , Cp 2 ZrCl(C · CPh) and 2 were identified by 1 H NMR (in nearly1 + 4 + 1 ratio respectively). After 24 h stirring and work-up, 2 was obtainedas a crystalline solid (0.840 g, 64% yield). With 3 equiv. LiC · CPh for 24 h,in the same experimental conditions, a red solution is obtained with theappearance of a paramagnetic Zr III species ( g = 1.997, a ( 91 Zr) = 37 G,20%) which broadens the 1 H NMR signals of the solution (the main peak observed at 5.6 ppm could not be assigned). Different experiments wereconducted in THF and in absence of daylight (to avoid the formation of thezirconacyclocumulene species) between (C 5 H 4 R) 2 Zr(C · CPh) 2 (R = Me,SiMe 3 ) and LiC · CPh. 13 C NMR spectroscopy shows the characteristic peak of the ( h 2 + 1,2-PhC 2 C · CPh) moiety at 208 and 205 ppm for R = Me andSiMe 3 , respectively which suggests the in situ formation of Li[(C 5 H 4 R) 2 Zr(C · CPh)( h 2 + 1,2-PhC 2 C · CPh)] (R = Me, SiMe 3 ) (forCp* 2 Ti( h 2 + 1,2-Me 3 SiC 2 C · CSiMe 311 two peaks were observed at 227 and205 ppm). Hydrolysis of the THF mixture with HCl gives the  Z/E  enynes(30 + 70).  ¶ It is of note that Cp 2 ZrCl 2 + 3 equiv. LiC · CPh in toluene at roomtemperature for 24 h selectively affords, after hydrolysis, the  Z  isomerwhereas the same reaction carried out in THF gives a mixture of  Z/E  isomers(40 + 60). The  Z  isomer was selectively obtained in THF when the reactionis carried out at 2 80 ° C. 9 ∑ Hydrolysis experiments with HCl on (C 5 H 4 R) 2 Zr( h 4 + 1,2,3,4-PhC N C N C N CPh) (R = H, Me, SiMe 3 ) give in toluene or in THF solutionnearly 100% of the  E  isomer PhCH N CH-C · CPh, in contradiction with thedescribed results in which the h 2 coordination is involved.**LiC · CBu t was added to 2 in THF; after stirring for 4 h, the solvent wasevaporated to dryness and replaced by toluene. Hydrolysis with HCl (3equiv. in solution in diethyl ether) gives Z enynes; 1 H NMR ( d   /ppm, CDCl 3 ,250 MHz), MS: PhCH N CHC · CBu t : 6.55, 5.69, (d, CH N CH,  J  = 12 Hz),1.32 (s, Bu t ), MS: 184; PhC · CCH N CHBu t : 5.87, 5.60, (d, CH N CH,  J  = 12Hz), 1.26 (s, Bu t ), MS: 184; PhCH N CHC · CPh: 6.70, 5.92, (d, CH N CH,  J  =12 Hz), MS: 204. When HCl hydrolysis was performed in THF, a mixtureof  Z/E  enynes was observed by GC/MS but not further characterized. ††  1 H and 13 C{ 1 H} NMR of the reaction show complex spectra in whichthree main cyclopentadienyl signals can be observed at 5.76, 5.71,5.67/105.0, 104.9, 104.7 ppm; low field quaternary carbons at 228, 225.9,208.2, 205.9, 203, 202 ppm were also observed.1H. S. Nalwa and S. Miyata,  Nonlinear Optics of Organic Molecules and Polymers , CRC Press, Boca Raton, FL, 1997.2( a ) A. de Meijeire, Top. Curr. Chem. , 1999, 201 , 000; ( b ) F. Diederich,in  Modern Acetylene Chemistry , ed. P. J. Stang and F. Diederich, VCH,Weinheim, 1995, p. 443; ( c ) F. Diederich and Y. Rubin,  Angew. Chem., Int. Ed. Engl. , 1992, 31 , 1101.3( a ) R. Choukroun, C. Lorber, B. Donnadieu, B. Henner, R. Frantz andC. Guerin, Chem. Commun. , 1999, 1099 and references therein; ( b ) R.Choukroun, B. Donnadieu, I. Malfant, S. Haubrich, R. Frantz, C. Guerinand B. Henner, Chem. 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Ed. Engl. , 1994, 33 , 1480.16A stable tweezer bimetallic alkynylcopper( I ) titanium acetylide has beencharacterized. M. D. Janssen, M. Herres, L. Zsolnai, D. Grove, A. L.Spek, H. Lang and G. van Koten, Organometallics , 1995, 14 , 1098. Scheme 1 1512 Chem. Commun. , 2000, 1511 – 1512
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