Substituent Effects as Probes of Structure and Bonding in Mononuclear Metallocenes

Complexes with Sterically Bulky Allyl Ligands: Insights into Structure and Bonding

“…[18] The Th[(SiMe 3 ) n C 3 H 5-n ] 4 compounds are stable up to 90°C (n = 1) or 124°C (n = 2) under an inert atmosphere. The stability of these complexes contrasts strongly with Th(C 3 H 5 ) 4 , which decomposes at 0°C. [3] Both molecules are fluxional on the 1 H NMR timescale, and η 3 i η 1 ligand rearrangements are involved in the interchange of their allylic protons.…”

“…[78] The coordination geometry around yttrium includes an oxygen atom from coordinated thf, four nitrogen atoms from the amido ligands, and an N···H contact (2.49 Å) from an amido hydrogen. Multistep insertions are likely involved in the reaction between NiAЈ 2 and PMe 3 , which yields tetramethyltetraphosphane, (MeP) 4 . The product was identified with 1 H, 13 C, and 31 P NMR spectra and its formation studied with DFT methods.…”

“…As a result, many of them are thermally unstable and difficult to handle. Wilke cites examples of these in his early review of homoleptic allyl complexes: [3] especially notable are Fe(C 3 H 5 ) 3 and Co(C 3 H 5 ) 3 , which decompose above -40°C, V(C 3 H 5 ) 3 , which explodes above -30°C, and Zr(C 3 H 5 ) 4 , Nb(C 3 H 5 ) 4 , and Ta(C 3 H 5 ) 4 , all of which decompose at 0°C. Even Ni(C 3 H 5 ) 2 decomposes within a day at room temperature under a nitrogen atmosphere.…”

“…Cyclopentadienyl chemistry has long benefited from the use of such substituted rings as C 5 Me 5 and C 5 H 3 (SiMe 3 ) 2 , which can be used to synthesize compounds of greater diversity and stability than is possible with Cp alone. [4][5][6] A similar approach is effective with the allyl ligand. The allyl anion can be substituted with a variety of alkyl, aryl, silyl, and siloxide groups, all of which can have substantial effects on the properties of their associated compounds.…”

“…For example, unlike the pyrophoric Ni(C 3 H 5 ) 2 , the trimethylsilylated derivative Ni[1,3-(SiMe 3 ) 2 -C 3 H 3 ] 2 only slowly decomposes in air (from hours to days). [17] In addition, the homoleptic thorium complexes Th[(SiMe 3 ) n C 3 H 5-n ] 4 (n = 1, 2) are stable to 90°C, [18] in contrast to Th(C 3 H 5 ) 4 , which decomposes at 0°C. In other cases, the presence of substituent groups aids in crystallization, so that solid-state structures may be obtained; calculations suggest that the X-ray crystal structure of the lithium dimer {Li[1,1Ј,3-(SiMe 3 ) 3 C 3 H 2 ]} 2 is related to that of the unsubstituted complex, which is known to be a dimer from cryoscopy, but which has not been structurally authenticated.…”