Reactions of Titanocene Bis(trimethylsilyl)acetylene Complexes with Carbodiimides: An Experimental and Theoretical Study of Complexation versus C–N Bond Activation

Abstract

The reaction of the low valent metallocene(II) sources Cp'(2)Ti(η(2)-Me(3)SiC(2)SiMe(3)) (Cp' = η(5)-cyclopentadienyl, 1a or η(5)-pentamethylcyclopentadienyl, 1b) with different carbodiimide substrates RN═C═NR' 2-R-R' (R = t-Bu; R' = Et; R = R' = i-Pr; t-Bu; SiMe(3); 2,4,6-Me-C(6)H(2) and 2,6-i-Pr-C(6)H(3)) was investigated to explore the frontiers of ring strained, unusual four-membered heterometallacycles 5-R. The product complexes show dismantlement, isomerization, or C-C coupling of the applied carbodiimide substrates, respectively, to form unusual mono-, di-, and tetranuclear titanium(III) complexes. A detailed theoretical study revealed that the formation of the unusual complexes can be attributed to the biradicaloid nature of the unusual four-membered heterometallacycles 5-R, which presents an intriguing situation of M-C bonding. The combined experimental and theoretical study highlights the delicate interplay of electronic and steric effects in the stabilization of strained four-membered heterometallacycles, accounting for the isolation of the obtained complexes.

Redox‐Disproportionation of a Decamethyltitanocene(III) Isonitrile Alkynyl Complex

“…Both isonitrile fragments in 2 display a significant deviation from linearity of the C≡ N −C(Xy) unit [C1‐N1‐C3 149.23(16), C2‐N2‐C11 171.08(17)°]. This observation has been reported before for the complex [Cp* 2 Ti(η 1 ‐CNMes) 2 ] [C‐N‐C(Mes) 142.4(2)/176.1(2)°; Mes=2,4,6‐trimethylphenyl] . A possible explanation was given by Filippou et al.…”

Reactions of Group 4 Metallocene Complexes with Mono‐ and Diphenylacetonitrile: Formation of Unusual Four‐ and Six‐Membered Metallacycles

“…These need to be stabilised by complexation, dimerisation or substitution of the carbon atom in the ring system. [26] Compound 7 is comparable to the complexes of titanium and zirconium with guanidinate ligands, which consist of substituents at the ring carbon atom as well. [27] The coupling product of two nitriles with an yttrium complex was published very recently.…”

Triazenido Complexes of Titanocene(III)

“…The bis(trimethylsilyl)acetylene ligand is known to serve as a spectator ligand and can easily be released under mild reaction conditions to in situ generate the reactive 14 electron fragment [Cp 2 Ti II ], which can be utilised to trap reactive fragments and stabilise unusual coordination geometries and ligand motifs. [8a] By this approach, some of us succeeded in isolating several pnictogen containing metallacycles featuring the general structural motifs Cp 2 Ti[RNENR] and Cp 2 Ti[R 2 PNPR 2 ] with E = C, P, S as illustrated in Figure . Except for Cp 2 Ti[Me 3 SiNSNSiMe 3 ] ( F ), this approach mostly led to the formation of Ti III compounds.…”

“…Generation of nitrogen containing four‐membered titanacycles starting from Cp 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 ) and E : SiMe 3 NCNSiMe 3 , F : Me 3 SiNSNSiMe 3 , G : [DippNPCl] 2 (Dipp = 2,6‐ i Pr 2 C 6 H 3 ), H : [Ph 2 PN(H)PPh 2 ] …”