DOI: 10.1002/chem.200801917 Structural Analysis of Zincocenes with Substituted Cyclopentadienyl Rings Rafael Fernndez,[a] Abdessamad Grirrane,[a] Irene Resa,[a] Amor Rodrguez,[a] Ernesto Carmona,*[a] Eleuterio lvarez,[a] Enrique Gutirrez-Puebla,[b] ngeles Monge,[b] Juan Miguel Lpez del Amo,[c] Hans-Heinrich Limbach,[c] Agustí Lleds,[d] Feliu Maseras,[d, e] and Diego del Ro[a, f] Abstract: New zincocenes [ZnCp’2](2– tion of 7, which yields a side-product ZnÀC bond of comparable strength to 5) with substituted cyclopentadienyl li- (C) upon attempted crystallisation. the ZnÀMe bond in ZnMe2. Zincocene gands C5Me4H, C5Me4tBu, Compounds 5 and 6 were also investi- 5 has dynamic behaviour in solution, 13 5 1 C5Me4SiMe2tBu and C5Me4SiMe3, re- gated by C CPMAS NMR spectrosco- but a rigid h /h (s) structure in the spectively, have been prepared by the py. Zincocenes 1 and 2 have infinite solid state, as revealed by 13C CPMAS reaction of ZnCl2 with the appropriate chain structures with bridging Cp’ li- NMR studies, whereas for 6 the differ- Cp’-transfer reagent. For a comparative gands, while 3 and 4 exhibit slipped- ent nature of the Cp’ ligands and of the structural study, the known sandwich geometries. Compounds 5 ring substituents of the h1-Cp’ group 5 1 [Zn(C5H4SiMe3)2](1), has also been in- and 6 have rigid, h /h (s) structures, in (Me and SiMe3) have permitted obser- 5 vestigated, along with the mixed-ring which the monohapto C5Me4SiMe3 vation for the first time of the rigid h / ACHTUNGRE 1 zincocenes [Zn(C5Me5)(C5Me4SiMe3)] ligand is bound to zinc through the h solution structure. Iminoacyl com- ACHTUNGRE 5 (6) and [Zn(C5Me5)(C5H4SiMe3)] (7), silyl-bearing carbon atom, forming a pounds of composition [Zn(h - ACHTUNGRE 1 ACHTUNGRE the last two obtained by conproportio- C5Me4R)(h -C(NXyl)C5Me4R)] result- nation of [Zn(CACHTUNGRE Me ) ] with 5 or 1,as ing from the reactions of some of the 5 5 2 Keywords: density functional calcu- appropriate. All new compounds were above zincocenes and CNXyl (Xyl= lations · iminoacyl · metallocenes · characterised by NMR spectroscopy, 2,6-dimethylphenylisocyanide) have structure elucidation · zinc and by X-ray methods, with the excep- also been obtained and characterised. Introduction cenes continues to be an important research theme. Cyclo- pentadienyl derivatives of most elements of the periodic Nearly six decades after the preparation of ferrocene[1] and table are known, including many main group elements, as the recognition of its sandwich structure,[2] study of metallo- well as the lanthanides and accessible actinides.[3–5] A large [a] Dr. R. Fernndez, Dr. A. Grirrane, Dr. I. Resa, Dr. A. Rodrguez, [d] Prof. A. Lleds, Prof. F. Maseras Prof. E. Carmona, Dr. E. lvarez, Dr. D. del Ro Unitat de Qumica Fsica, Edifici Cn Instituto de Investigaciones Qumicas Universitat Autnoma Departamento de Qumica Inorgnica Bellaterra, 08193 Barcelona (Spain) Universidad de Sevilla-Consejo Superior [e] Prof. F. Maseras de Investigaciones Cientficas Institut of Chemical Research of Catalonia Avenida Amrico Vespucio 49, 41092 Sevilla (Spain) Avenida Pasos Catalans 16, 43007 Tarragona (Spain) Fax : (+34)954460565 [f] Dr. D. del Ro E-mail: [email protected] current address: SRI [b] Prof. E. Gutirrez-Puebla, Prof. Monge 333 Ravenswood Avenue Instituto de Ciencia de Materiales de Madrid Menlo Park, 94025 CA (USA) Consejo Superior de Investigaciones Cientficas Supporting information for this article is available on the WWW Campus Cantoblanco, 28049 Madrid (Spain) under http://dx.doi.org/10.1002/chem.200801917. [c] Dr. J. M. Lpez del Amo, H.-H. Limbach Institut fr Chemie and Biochemie Freie Universitt Berlin Takustrasse 3, 14195 Berlin (Germany) 924 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2009, 15, 924 – 935 FULL PAPER variety of cyclopentadienyl ligands may be used,[6] ranging ous work on beryllocenes, which resulted in the structural ACHTUNGRE ACHTUNGRE from the parent C5H5 and its alkyl-substituted derivatives, characterization of [Be(C5Me5)2], [Be(C5Me4H)2] and ACHTUNGRE ACHTUNGRE [11a] exemplified by the widely utilised C5Me5, to the bulkier, so- [Be(C5Me5)(C5Me4H)], we have undertaken a systematic [6b] called supracyclopentadienyls, for example, C5Ph5 and study of the structures of new zincocenes, of both polymeric C5iPr5. Recently, perarylated cyclopentadienyls C5Ar5 of and monomeric nature. Our original aim was the synthesis [7] 5 1 substituted aryl groups, for instance Ar=4-nBu-C6H4,or and characterization of a zincocene with a rigid h /h (s) [15] 3,5-tBu2C6H3, referred to as superbulky cyclopentadienyls, structure (d). Here we give a full report of these findings have imparted renewed impetus to the field by providing and provide synthetic, reactivity and structural data for new unexpected structures and reactivity, as well as remarkable zincocenes derived from the C5Me5,C5Me4H, C5Me4tBu, [8] stability to their corresponding metallocenes. C5Me4SiMe2tBu, and C5Me4SiMe3 rings. For the sake of With few exceptions, transition-metal metallocenes completeness, the previously reported compound 5 [MCp2’](Cp’ is used in this paper as a general representa- [Zn(C5H4SiMe3)2], shown by Haaland et al. to posses an h / tion for a cyclopentadienyl ligand) have a ferrocene-type h1(s) structure in the gas phase,[12a] has also been character- structure (a). In the analogous metallocenes of divalent f ised by X-ray crystallography. Results and Discussion Most beryllocenes and zincocenes known to date exhibit the slipped-sandwich structure[11,12] c. In the gas phase [Zn(C5H4SiMe3)2](1), was shown by Haaland and co-work- ers[12a] to have h5/h1(s) coordination of the Cp’ rings, with the zinc atom bonded to the silyl-bearing carbon atom of elements,ACHTUNGRE the rings coordinate also in the h5 fashion, al- the h1 ligand, a ZnÀC bond length of 1.95 and an angle of though unusually bent structures are typically observed (b; 1108 between the ZnÀC bond and the ring plane. Since the see also reference [8a] for somewhat different geometries). solid-state structure of 1 has not been reported, we consid- Cyclopentadienyl derivatives of the main-group elements ered of interest its determination by X-ray crystallography. offer a rich structural diversity since they may adopt a varie- Zincocene 1 was prepared by a slight modification of the lit- [12a] ty of structures, including the slipped-sandwich geometry c. erature procedure, reacting LiC5H4SiMe3 and ZnCl2 in This structure is often represented as h5/h1(p), in which tetrahydrofuran (THF) for 12 h. Following evaporation of h1(p) implies metal coordination through one carbon atom the solvent under vacuum, extraction with pentane and crys- of the ring by means of the p cloud and consequently planar tallization afforded the desired metallocene with spectro- or nearly planar coordination geometry of the sp2-hybridised scopic features identical to those already published.[12a] For carbon atom, giving an essentially parallel arrangement of the sake of completion, it is worth mentioning that the two the two Cp’ ligands. rings of 1 are equivalent in solution (see below for the dy- Zincocenes conform to this structural assortment. In con- namic behaviour of these molecules) and yield 1H NMR res- trast, the recent isolation of the ZnÀZn bonded dimetallo- onances with d= 0.05 (SiMe3), 6.26 and 6.61 ppm (CH). In ACHTUNGRE 5 5 [9] 13 1 cenes, [Zn2(h -C5Me5)2] and [Zn2(h -C5Me4Et)2] places the C{ H} NMR spectrum corresponding resonances are them, for the time being, in an unique position among all found at d=À0.2 (SiMe3), 114.5 and 117.7 ppm (CH), while metallocenes. A common feature of zincocenes is their low the silicon-bound carbon atom resonates at 87.2 ppm. As hapticity count, often h1 or h2. Thus, in the solid state the discussed later for related compounds these chemical shift ACHTUNGRE parent zincocene, [Zn(C5H5)2], features a structure consist- values are intermediate between those corresponding to the 1 5 ing of an infinite chain of zinc atoms bridged by C5H5 two rings of a rigid structure, with h and h cyclopenta- groups, with each zinc atom surrounded by one terminal and dienyls.ACHTUNGRE 2 [10a] ACHTUNGRE [10a] two bridging ligands, all with h binding. In the gas- As for the parent zincocene [Zn(C5H5)2], compound 1 phase[10b] the molecules have the h5/h1(p) coordination c, has a polymeric structure in the solid state that consists of [11] which is also characteristic of beryllocenes. The molecular infinite chains of zinc atoms bridged by C5H4SiMe3 ligands. ACHTUNGRE [12a,b] ACHTUNGRE [12b] zincocenes [Zn(C5Me5)2], [Zn(C5Me4Ph)2] and [Zn- The asymmetric unit consists of two zinc atoms that are not ACHTUNGRE [12c] (C5iPr4H)2], have a slipped-sandwich geometry too, while equivalent by symmetry, each coordinated to three Cp’ li- zincocenes of 1,2-diaza-3,5-diborolyl ligands have a h1(p)/ gands in a slightly different manner. Each zinc atom h1(p), or h3/h3 coordination.[13] Even in an ansa-zincocene re- (Figure 1) has one terminal and two bridging Cp’ groups. cently reported by Erker and co-workers, in which the ri- For example, with reference to Zn1, the terminal ring is gidity of the ligand might be expected to enforce higher bound in h1(p) fashion or close to it. Thus, the Zn1ÀC3 dis- hapticity, the coordination of the two indenyl units is of the tance of 2.060(9) and the angle of about 99.78 formed by h1/h2(ACHTUNGREs,p) type.[14] the Zn1ÀC3 bond with the plane of this ring are typical for Continuing our investigations of main-group metallocenes this type of coordination.[12] The distances between Zn1 and and with the objective of broadening the scope of our previ- the carbon atoms C4 (2.533(9) ) and C2 (ca.