Decamethylsilicocene Chemistry:  Unprecedented Multistep Reactions of a Silicon(II) Compound with the Heterocumulenes CO₂, COS, CS₂, and RNCS (R = Methyl, Phenyl)

Abstract

In the reaction of the nucleophilic decamethylsilicocene, ((Me5C5)2Si (1), with the electrophilic heterocumulenes CO2, COS, CS2, and RNCS, multistep processes are observed, which in most cases proceed via several highly reactive intermediates. In all reactions, the formal oxidation state of the silicon atom changes from +2 in 1 to +4, and the hapticity of the pentamethylcyclopentadienyl ligands changes from η5 to η1. In the reaction of 1 with CO2, COS, or RNCS, double-bond species of the type (Me5C5)2SiX (X = O, S) are formed, which are stabilized via different routes. Thus, reaction of 1 with CO2 in toluene as solvent finally leads to the spiro compound [(Me5C5)2SiO2]2C (4), whereas in pyridine as solvent, the eight-membered heterocycle [(Me5C5)2SiO2CO]2 (5) is formed. The dithiadisiletane [(Me5C5)2SiS]2 (9) results from the reaction of 1 with COS. Dithiasiletane derivates of the type (Me5C5)2SiS2CNR (10, 11) are the final products from the reaction of 1 with RNCS (R = CH3, C6H5). Multistep rearrangement processes have to be postulated to explain the formation of the dithiadisiletane derivate 15 in the surprising reaction of 1 with CS2; ligands that initially are bonded to the silicon (Me5C5) and to the carbon atom (S) have to be completely exchanged to build up the final product. The silaheterocycles 4, 5, 10, and 15 and also some of the basic molecular framework have been unknown in the literature. The crystal strucutres of 4, 5, 10, and 15 were determined by X-ray crystallography and are presented.

Where silylene–silicon centres matter in the activation of small molecules

“…Kira demonstrated that the dicoordinate dialkylsilylene 43, 2,2,5,5-tetrakis(trimethylsilyl)-silacyclopentane-1,1-diyl, reacts with CO 2 smoothly at room temperature, followed by hydrolysis by the water contamination in MeOH, to give the corresponding bis(silyl)carbonate 44 in high yields (Scheme 20). 51 DFT calculations showed that the reaction involves the formation of a SiQO bonded intermediate, which is similar to that of the decamethylsilicocene reported by Jutzi et al 40 As for the bis(amidinato)silylene 45 (Scheme 21), its reaction with an excess of N 2 O at low temperatures affords the dinuclear five-coordinate Si IV complex 46, while the mononuclear sixcoordinate Si IV complex 47 is obtained by treatment of 45 with an excess of CO 2 at room temperature. 52 The mechanism can be rationalised through the formation of a five-coordinate silanone species, followed by its dimerisation to give 46 Heterocyclic silylene 56a featuring a particularly electronrich Si centre reacts smoothly with N 2 O in THF at À80 1C to give the silanone product 57a (Scheme 22), which is stable below À50 1C.…”

Cycloaddition versus Cleavage of the C=S Bond of Isothiocyanates Promoted by Digallane Compounds with Noninnocent α‐Diimine Ligands

“…[7d] Similarly,J utzi et al found that Cp* 2 Si can cleave the C=Sb ond of RNCS to give the S-bridged dimer [Cp* 2 Si(m-S)] 2 . [33] Although C=Sbondcleavage of isothiocyanates by transition metal complexes, for example, [Cp*(CO)(H)Ru=Si(H){C(SiMe 3 ) 3 }], [34] [Cp*Co(H 2 C= CH 2 ) 2 ], [35] [Cp 2 (CO) 5 W 2 (m-h 1 :h 2 -CH 2 CO)], [36] and [(meso-o-C 6 H 4 (dpe) 2 )Mo(dpm)], [37] has previously been reported, examples of C=Sb ond activation promoted by main group compounds remainparticularly rare. [12,38] Products of reaction type III withboth cycloaddition and cleavage of the C=Sb ond of isothiocyanates: [Na(THF) 2 ] 2 [L 1 (PhN=CÀS)Ga(m-S) 2 Ga(SÀC=NPh)L 1 ](6) and [L 1 (PhN=CÀS)Ga(m-S)Ga(SÀC=NPh)L 1 ]( 7)…”

Reversible CO2 Addition to a Si=O Bond and Synthesis of a Persistent SiO2–CO2 Cycloadduct Stabilized by a Lewis Donor–Acceptor Ligand

“…To the best of our knowledge,this is the first report describing the reversible addition of CO 2 on stable silanones. [14,15] Nonetheless,afew examples of stable sila-carbonates (X and XI) [16] and sila-dicarbonate XII, [17] synthesized by the reactions of transient silanones or SiO 2 complexes with CO 2 ,h ave recently been characterized. AC DCl 3 solution of base-stabilized sila-b-lactone 1 [13] readily reacts with CO 2 (4 bars) in aJ -Young NMR tube at À50 8 8C, affording the [2+ +2] cycloadduct 2 (Scheme 1).…”