We present the synthesis and characterization of disila- and distanna ansa half-sandwich complexes of Group 6 transition metals. These compounds exhibit high ring strain within the ansa bridge, which is the key factor for the insertion of elemental chalcogens.

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The reaction of the dichlorogermane Me2GeCl2 and stannanes R2SnCl2 (R = Me, Bu) with the alkali tungsten salts M[(η5‐C5R′5)L(OC)2W] (L = CO, PPh3; M = Li, Na; R′ = H, Me) yields via alkali salt elimination a range of novel chlorostannyl‐ and chlorogermyl‐functionalized tungsten complexes of the general formula [(η5‐C5R′5)L(OC)2W(ER2Cl)] (R′ = H, Me; L = CO, PPh3; E = Ge, Sn; R = Me, Bu) (3a–e). The use of the phosphane‐substituted tungsten anion Na[(η5‐C5Me5)(Ph3P)(OC)2W] (1c) and Me2SnCl2 leads to a mixture consisting of the mono‐ (3e) as well as the di‐substituted stannyl compound [{(η5‐C5H5)(Ph3P)(OC)2W}2(SnMe2)] (4). Access to 3a is also given by reaction of ClMe2Sn–C5H5 (5) with [(MeCN)3W(CO)3] which includes chemoselective tin shift from the cyclopentadiene to the tungsten atom. In addition, a successive chlorination of [(η5‐C5H5)(OC)3W(SnMe3)] (6) via [(η5‐C5H5)(OC)3W(SnMe2Cl)] (3a) and [(η5‐C5H5)(OC)3W(SnMeCl2)] (7) to [(η5‐C5H5)(OC)3W(SnCl3)] (8) is presented. All new compounds have been fully characterized by elemental analyses and in solution by IR and multinuclear NMR spectroscopy. The crystal structures of complexes 3b–d and 8 were presented and discussed, showing bond lengths of 2.6272(4) Å for Ge–W, 2.7959(5) (3b), 2.7866(3) (3d) and 2.7244(3) (8) Å for the Sn–W bonds.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

We report the introduction of two stannyl groups into a half-sandwich tungsten complex and their subsequent functionalization in order to generate useful precursors for the formation of diverse ansatype tungsten complexes. Bis-stannylation is achieved by treatment of the dilithiated species Li-[W(η 5 -C 5 H 4 Li)(CO) 3 ] (7) with 2 equiv of Me 3 SnCl, yielding [{Me 3 Sn(η 5 -C 5 H 4 )}(OC) 3 W(SnMe 3 )] (8). Successive chlorination is achieved by use of Me 2 SnCl 2 and SnCl 4 3 2OEt 2 and enables the selective formation of [{Me 3 Sn(η 5 -C 5 H 4 )}(OC) 3 W(SnMe 2 Cl)] ( 10), [{ClMe 2 Sn(η 5 -C 5 H 4 )}(OC) 3 -W(SnMe 2 Cl)] ( 11), and [{ClMe 2 Sn(η 5 -C 5 H 4 )}(OC) 3 W(SnMeCl 2 )] ( 12). The reaction of 11 with sodium amalgam gives a product mixture, consisting of the tristanna-bridged ansa complex [{η 1 -SnMe 2 -SnMe 2 -SnMe 2 -(η 5 -C 5 H 4 )}(CO) 3 W] (13) and the cyclic dinuclear tungsten compound [{Me 2 Sn-(η 5 -C 5 H 4 )}-(OC) 3 W] 2 ( 14). Ring closure of 12 was achieved upon reaction with Na 2 S to yield [{η 1 -Sn(Cl)Me-S-SnMe 2 -(η 5 -C 5 H 4 )}(CO) 3 W] (15), which displays a chiral, tungsten-bound tin center. All new compounds have been fully characterized by elemental analyses and, in solution, by IR and multinuclear NMR spectroscopy. The crystal structures of complexes 8, 11, 12, 14, and 15 were presented and discussed, showing Sn-W bond lengths of 2.8481(5) (8), 2.7586(3) (11), 2.7256(3) (12), 2.8180(3) ( 14), and 2.7662(2) A ˚(15).

The novel bimetallic micro-diboranyl-oxycarbyne bridged platinum-tungsten complex [W{eta(1),micro-CO-B(NMe(2))-B(NMe(2))-(eta(5)-C(5)H(4))}(CO)(2){Pt(PPh(3))(2)}] (W-Pt) () has been synthesised by a two-step reaction, starting from the dilithiated half-sandwich compound Li[W(eta(5)-C(5)H(4)Li)(CO)(3)] () via the ansa-diboranyl-oxycarbyne tungsten complex [W{eta(1)-CO-B(NMe(2))B(NMe(2))(eta(5)-C(5)H(4))}(OC)(2)] () by use of stoichiometric amounts of B(2)(NMe(2))(2)Br(2) and [Pt(eta(2)-C(2)H(4))(PPh(3))(2)], respectively.

A range of potential boron-based ligand precursors has been synthesized starting from [{Br 2 B(η 5 -C 5 H 4 )}Mn(CO) 3 ] (1) via salt elimination reactions. These comprise ligand precursors suitable for the preparation of i) ansa-metallocenes such as [CymB(η 1 -C 5 H 5 ) 2 ] (2), [CymB(1-C 9 H 7 ) 2 ] (3a), and [CymB(3-C 9 H 7 ) 2 ] (3b), ii) constrained geometry complexes such as [CymB(Br)N(H)tBu] (5) as well as iii) ansa-diamido complexes such as [CymB{N(H)Ph} 2 ] (4) and [CymB{N(H)tBu} 2 ] (6) (Cym ϭ

The reaction of the 1,2-dihalodiborane(4) B 2 (NMe 2 ) 2 Cl 2 with the lithium tungsten salts Li[(η 5 -C 5 H 5 )(R 3 P)(OC) 2 W] [R = Me (3a), Ph (3b)] yields via alkali salt elimination the phosphinesubstituted diborane(4)yl tungsten complexes [(η 5 -C 5 H 5 )(R 3 P)(OC) 2 W-{B(NMe 2 )-B(NMe 2 )Cl}] [R = Me (4a), Ph (4b)]. Both compounds have been fully characterized in solution by NMR and IR spectroscopy and 4a additionally by X-ray diffraction analysis.

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