FULL PAPER Four-Coordinate Group-14 Elements in the Formal Oxidation State of Zero – Syntheses, Structures, and Dynamics of [{(CO) 5 Cr} 2 Sn(L 2 )] and Related Species  Peter Kircher, Gottfried Huttner*, Katja Heinze, Berthold Schiemenz, Laszlo Zsolnai, Michael Büchner, and Alexander Driess Anorganisch-Chemisches Institut der Universität Heidelberg Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany Fax: (internat.) + 49(0)6221/545707 Received February 2, 1998 Keywords: Germanium / Tin / Lead / 119 Sn NMR / Dynamic NMR / Salt metathesis The sodium salts Na 2 [{(CO) 5 M} 2 EX 2 ] (M = Cr, Mo, W; E = compounds (2b, 2c) are able to rotate by a full 180° turn- around with respect to one another. This process must Ge, Sn, Pb; X = Cl, I, OOCCH 3 ) react with 2,2’-bipyridine (bipy) to form neutral compounds [{(CO) 5 M} 2 E(bipy)] (E = Sn: involve complete de-coordination of at least one of the two nitrogen donors in again at least one of the chelate cycles, 1a–1c; E = Ge: 3a; E = Pb: 4). 1,10-Phenanthroline (phen) analogues of compounds 1a–1c and 3a [{(CO) 5 M} 2 E(phen)] the activation energy for this process being around 60 kJ/ mol. By 119 Sn-NMR spectroscopy of almost all of the tin (E = Sn: 1d–1f, E = Ge: 3b) are as well accessible. The 2,2’- bipyridine ligand in 1 may be formally replaced by two compounds described it is shown that equilibria between [{(CO) 5 M} 2 Sn(L 2 )] and [{(CO) 5 M} 2 Sn(L)] + L exist in all cases. pyridine (py) ligands resulting in [{(CO) 5 M} 2 Sn(py) 2 ](1g:M= Cr, 1h: M = W). The bis-bidentate ligand 2,2’-bipyrimidine From the temperature dependence of the δ values it is concluded that the activation barriers for this association/ (bpmd) is found to coordinate just one [{(CO) 5 M} 2 Sn] entity in [{(CO) 5 M} 2 Sn(bpmd)] (2b:M= Cr, 2c: M = W). The dissociation process is below 10 kJ/mol. The structures of all new compounds are documented by X-ray analyses and all biimidazolato (biim) ligand binds two [{(CO) 5 Cr} 2 Sn] moieties in [{(CO) 5 Cr} 2 Sn(biim)Sn{Cr(CO) 5 } 2 ] 2– , 2a. It is compounds are characterized by the usual analytical and spectroscopical techniques. shown by 1 H-NMR that the pyrimidine entities in these Na[BPh 4 ] the highly reactive sodium salts Introduction [Na(solv) x ] 2 [{(CO) 5 M} 2 SnCl 2 ] are formed [4] . The difference in reactivity of these two types of salts is illustrated by the The chemistry of low-valent main-group compounds may observation that the phosphonium salts do not react with considerably be expanded by using organometallic protec- sodium 8-oxoquinolate, Na[C 9 H 6 NO], while the sodium tive groups to electronically and sterically inhibit the de- salt [Na(solv) x ] 2 [{CO) 5 Cr} 2 SnCl 2 ] instantaneously does [4] . composition of such species. Thus while neither Bi 2 nor The resulting anion [{(CO) 5 Cr} 2 Sn(oxinato)] - contains a Sn 6 2- are known as such at ambient temperature their or- tetrahedrally coordinated tin center (formal oxidation state: ganometallic derivatives [{(CO) 5 W} 3 Bi 2 ] [1] and Sn 0 ) with two coordination positions occupied by the [{(CO) 5 Cr} 6 Sn 6 ] 2- [2] are well characterized species. In order anionic chelate ligand [4] . to exploit the unconventional chemistry of compounds con- We report here that an analogous procedure allows for taining low-valent tin aggregates embedded in an or- the replacement of the two halide substituents in A by neu- ganometallic matrix, starting materials which contain reac- tral nitrogen-based chelate ligands leading to neutral ad- tive tin-halide bonds and have the tin centers already coor- ducts of types 1 and 2 which as well contain tin in the for- dinated to organometallic building blocks should be useful. mal oxidation state of zero. Analogous reactivity is ob- With this idea in mind syntheses of various salts containing served for the homologues of type A anions containing ger- anions of type A (Figure 1) had been developed [3] [4] . manium or lead instead of tin. 2,2'-Bipyridine or 1,10- Figure 1. Anions of type A phenanthroline adducts of Ge 0 , 3, and Pb 0 , 4, stabilized by coordination to two [(CO) 5 Cr] groups are thus obtained. Results and Discussion a) Compounds 1 Containing 2,2'-Bipyridine or 1,10-Phenanthroline as Chelating Ligands It had been found that the salts formed with [Ph 4 P] + counter ions are quite unreactive and correspondingly in- THF solutions of the sodium salts of the anions of type A, [{(CO) 5 M} 2 SnCl 2 ] 2- , are prepared from definitely stable at room temperature under an inert atmos- phere [4] . When, however, these salts are metathesized with [Ph 4 P] 2 [{(CO) 5 M} 2 SnCl 2 ] by salt metathesis with Na[BPh 4 ] Eur. J. Inorg. Chem. 1998, 703-720  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998 1434-1948/98/0606-0703 $ 17.50+.50/0 703