Synthesis of ((Bu3SiNH)-Bu-t)(2)ClW equivalent to WCl((NHSiBu3)-Bu-t)(2) and its degradation via NH bond activation

Treatment of NaW2Cl7(THF)(5) with 4 equiv of (Bu3SiNHLi)-Bu-t afforded the C-2 W(III) dimer [((Bu3SiNH)-Bu-t)(2)WCl](2) (1, d(W equivalent toW) = 2.33 7(2) Angstrom), which is a rare, primary amide M2X4Y2 species. Its degradat ion provided evidence of NH bond activation by the ditungsten bond. Additio n of 2 equiv of (Bu3SiNHLi)-Bu-t or (TlOSiBu3)-Bu-t to 1 yielded H-2 and hy dride ((Bu3SiN)-Bu-t)(2)((Bu3SiNH)-Bu-t)WH (2, d(WH) = 1.67(3) Angstrom) or ((Bu3SiN)-Bu-t)(2)((Bu3SiO)-Bu-t)WH (3). Thermolysis (60 degreesC, 16 h) o f 1 in py gave ((Bu3SiN)-Bu-t)(2)WHCl(py) (4-py, 40-50%)((Bu3SiN)-Bu-t)(2)W Cl2(py) (6-py, 10%), and ((Bu3SiN)-Bu-t)(2)HW(mu -Cl)(mu -H)(2)W((NSiBu3)-B u-t)py(2) (5-py(2), 5%), whereas thermolysis in DME produced ((Bu3SiN)-Bu-t )(2)WCl(OMe) (7, 30%), ((Bu3SiN)-Bu-t)(2)WCl2 (6, 20%), and ((Bu3SiN)-Bu-t) (2)HW(mu -Cl)(muH)(2)W((NSiBu3)-Bu-t)DME (5-DME, 3%). Compound 7 was indepe ndently produced via thermolysis of 4-py and DME (-MeOEt, -py), and THF and ethylene oxide addition to hydride 2 gave ((Bu3SiN)-Bu-t)(2)((Bu3SiNH)-Bu- t)(WOBu)-Bu-n (8) and ((Bu3SiN)-Bu-t)(2)((BuSiNH)-Bu-t-Si-3)WOEt (9), respe ctively. Dichloride 6 was isolated from SnCl4 treatment of 1 with the loss of H-2. Sequential NH bond activations by the W-2 core lead to "((Bu3SiN)-B u-t)(2)WHCl' (4) and subsequent thermal degradation products. Thermolysis o f 1 in the presence of H2C=(CHBu)-Bu-t and PhC equivalent to CPh trapped 4 and generated ((Bu3SiN)-Bu-t)(2)W((neo)Hex)Cl (10) and a a similar to6:1 mi xture of ((Bu3SiN)-Bu-t)(2)WCl(cis-CPh equivalent to CPhH) (11-cis) and ((B u3SiN)-Bu-t)(2)WCl(trans-CPh=CPhH) (11-trans), respectively. Thermolysis of the latter mixture afforded ((Bu3SiNH)-Bu-t)((Bu3SiN)-Bu-t)WCl(eta (2)-PhC CPh) (12) as the major constituent. Alkylation of 1 with MeMgBr produced (( Bu3SiN)-Bu-t)(2)W(CH3)(2) (13), as did addition of 2 equiv of MeMgBr to 6. X-ray crystal structure determinations of 1, 2, 5-py(2), 6-py, 11-trans, an d 12 confirmed spectroscopic identifications. A general mechanism that feat ures a sequence of NH activations to generate 4, followed by chloride metat hesis, olefin insertion, etc., explains the formation of all products.