Intramolecular Activation of a Disila[2]molybdenocenophanedihydride: Synthesis and Structure of a [1],[1]Metalloarenophane

Abstract

Metallocenophanes have attracted increasing attention in recent years, as strained ansa complexes have become pivotal precursors for organometallic polymers prepared by ringopening polymerization (ROP), whereas unstrained metallocenophanes, especially those derived from Group 4 metals, serve as catalysts for olefin polymerization.[1]The structural and electronic properties and the particular reactivity of ansa complexes are in the focus of current research. The reactivity of the EÀC ipso bond (E = bridging element, C ipso = ipso carbon atom of the cyclopentadienyl ring) is of major importance for ROP, which can be induced thermally, by interaction with nucleophiles, or by latetransition-metal catalysts.[1a-e] Furthermore, ligand exchange reactions, which play a role in catalytic processes, [1f-h, 2] as well as haptotropic shifts of cyclopentadienyl ligands under different conditions [3] are being intensely studied. [2]Metallocenophanes, which are not commonly susceptible to ROP owing to their lower molecular strain, nevertheless attracted considerable attention because of their pronounced propensity to oxidatively add to coordinatively unsaturated complexes of late-transition-metal elements through the bridging EÀE (E = B, Si, Sn) moiety. Owing to the facile activation of the E À E bond by, for example, Pd 0 and Pt 0 , subsequent insertions of various unsaturated organic substrates have been achieved. In 1992, Manners and coworkers reported the first Pd-catalyzed insertion of alkynes into the SiÀSi bridge of tetramethyldisila[2]ferrocenophane, [4] Herberhold et al. described in 1997 the first oxidative addition of a Pt 0 fragment into the SnÀSn bridge of an ansaferrocene and the subsequent insertion of an alkyne, [5] whereas our group accomplished oxidative additions of Pt 0 fragments as well as homogeneously and heterogeneously catalyzed insertions of alkynes and diazobenzene into BÀB and SiÀSi bonds of various [2]metalloarenophanes. [6] Motivated by this facile activation of the EÀE bridge, we wondered whether a corresponding oxidative addition can be achieved intramolecularly and turned our attention to tetramethyldisila[2]molybdenocenophanedihydride (1) as a promising starting material. Herein we report the synthesis and full characterization of this species and its conversion into an unprecedented twofold-bridged [1],[1]metalloarenophane.Compound 1 was synthesized by dilithiation of 1,2-bis(cyclopentadienyl)tetramethyldisilane in toluene/diethyl ether (9:1) at 0 8C and subsequent reaction with MoCl 5 at À78 8C in the presence of NaBH 4 as a reducing agent in THF/ hexane (4:1) (Scheme 1).The very air-sensitive but moisture-stable compound 1 was obtained as a yellow solid in 29 % yield and was characterized by multinuclear NMR spectroscopy in solution. Two characteristic virtual triplets for the C 5 H 4 ligands at d = 4.72 and 4.70 ppm, one singlet for the methyl groups at d = 0.17 ppm, and one signal for the hydrogen atoms at d = À8.20 ppm are observed in the 1 H NMR spectrum, thus indicating C 2v symmetr...

Simultaneous Fragmentation and Activation of White Phosphorus

“…For the SiMe 2 groups a singlet at δ =0.27 ppm and a triplet at δ =0.34 ppm, showing a hydrogen–phosphorus coupling constant of J PH =5.88 Hz are observed. The 29 Si NMR spectrum exhibits one signal at δ =−2.9 ppm, the shift of which is in good agreement with that observed for [Cp*(CO) 2 FeP(Ph)SiMe 2 Ph]14 and is shifted to higher field with respect to that of starting compound 1 (91.0 ppm) 9. Due to the coupling of the silicon atom to both phosphorus atoms ( 1 J SiP and 2 J SiP ), the signal is split into a virtual triplet.…”

“…Likewise, MoP separations (260.93(4) and 261.81(4) pm) are markedly longer than those in 3 (255.0 and 252.6 pm) 12. Moreover, the angles ( β ) between the SiC ipso bond axes and the planes of the C 5 H 4 ligands (19.4 and 19.1°) are substantially smaller than those found in 1 (48.7 and 48.9°), but larger than those of the unstrained complex [((C 5 H 5 )SiMe 2 ) 2 MoH 2 ] (2.5 and 2.1°), indicating a decrease in molecular strain 9. In keeping with this observation, the tilt angle ( α ; angle between the planes of the C 5 H 4 rings, 41.50(5)°) is comparable to that of 3 (43.08°),12 but considerably larger than that of 1 (20.48(7)°) 9.…”

“…Therefore, it may be highly profitable to provide a suitable compound comprising one or two reactive TME bond(s), thus combining P 4 degradation by the TM with simultaneous formation of useful PE bonds. To test the idea, we turned our attention towards the highly strained [1],[1]‐disilamolybdenocenophane ( 1 ) 9. In our hands, this particular complex proved to have three reactive centers, which are located at the central Mo and both Si atoms9, and are utilized in its reaction with tert ‐butylisonitrile to form the unprecedented ansa ‐Fischer‐type carbene complex 2 (Scheme ) 10…”

Photochemistry of Transition Metal Hydrides

“…The metallocene 1,1-disilamolybdenocenophane was synthesized by the photochemical reaction of the dihydride analogue and H 2 reductive elimination with intramolecular Si–Si oxidative addition (Scheme ). , …”

Influence of Cyclopentadienyl Ring‐Tilt on Electron‐Transfer Reactions: Redox‐Induced Reactivity of Strained [2] and [3]Ruthenocenophanes

“…18 Furthermore, recent investigations illustrated how changes in the redox state of [ n ]metallocenophanes can alter their ansa structure and electron distribution, as observed through the synthesis and reactivity of a [1]ferrocenophanium ion 4 + (Figure 2). 19 In addition, several other reactivity modes for strained [ n ]metallocenophanes that involve reactivity at the metal centre have been identified 11d. 20…”