Transcript Slide 1

Reversible reactions across the M-C bond of lanthanide NHC
complexes to form new N-E and C-E bonds
A. I. Germerotha, Z. R. Turnera, I. J. Caselya, R. M. Bellabarbab, R. P. Toozeb, P. L. Arnolda,*
a
School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK
bSasol
Technology, Purdie Building, North Haugh, St. Andrews, KY16 9ST, UK
[email protected]
Many organometallic f-block complexes are highly effective at the activation of small molecules including alkanes, although subsequent functionalisation chemistry can be hampered by the
difficulty of functional group incorporation chemistry for these metals.[1] We have been studying ligand systems that might bring in a second substrate.
N-heterocyclic carbene ligands (NHCs) are versatile, neutral, two-electron σ-donors which are used in a wide variety of organometallic chemistry. The carbene donor atom in an NHC is
stabilised by the two adjacent heterocyclic nitrogen atoms. In recent years, bidentate saturated NHC-ligands bearing an anionic alkoxide tether have been developed by our group.[2] The tether
allows the ligand to be ‘anchored’ to the metal centre, so that the hemilabile carbene can be retained in the metal’s coordination sphere. The syntheses of mono or bisligand f-block element
carbene complexes are therefore possible.[3] We plan to use the combination of the Lewis acidic metal with the labile carbene to activate small molecules.
Carbene amido and alkyl complexes
Synthesis of the bright yellow
monoligand and bisligand
cerium complexes, colourless
group 3 complexes and the
dark blue monoligand uranium
analogue
have
been
accomplished.
The proligand
HL can be
made in five
steps from
ArNH2 in 68 %
yield.
HL
Addition-elimination across the M-CCarbene bond
X-ray structure of U(LSi)N’’2I
X-ray structure of
Li(thf)[(L)Sc(CH2Si’)3
X-ray structure of Ce(L)N’’2
For E = CPh3
the first C-C
bond
forming
reaction yet on
organolanthanide
complexes
X-ray structure of Y(L)(CH2Si’)2
Products formed
● N-Si
●N-B
●N-P
●N-Sn
●C-C
●C-Si
● Reaction of small molecules of the form E-X (E = CR3, SiR3, PR2, BR2, SnR3; X = halide, pseudohalide) with M(L)R2 (M = Y, Ce, U) results in the addition across the neutral metal carbene
bond, adding E to the carbene moiety and X to the metal as schematically shown in M(LE)RX2[4]
● The metal carbene is then reformed by elimination of E-R to form M(L)XR or M(L)R2 thus incorporating additional groups such as boranes, silanes, phosphanes or stannanes into
compounds that are active for σ-bond metathesis
● M(L)XR complexes can in the case of M = Y, Ce reform the starting material M(L)R2 by reacting it with 1 eq of KR or LiR
● When the [Li(thf)[(L)MR3] (M = Sc, Y) compound is treated with 1 eq of E-X (E = CR3, SiR3, X = halide, pseudohalide) the aforementioned complex M(LE)R2X is formed.
● E-X reagents that were used in our studies include Me3SiI, Me3SiCl, Me3SiN3, But3SnCl, (B-I)-9-BBN, ClCPh3 and ClPPh2
● All addition-elimination reactions of these substrates across the metal-carbene bond are reversible
References
[1]
[2]
[3]
[4]
P. L. Arnold, I. J. Casely, Chem. Rev.,2009, 109, 3599.
P. L. Arnold, I. J. Casely, Z. R. Turner, C. D. Carmichael, Chem. Eur. J., 2008, 14, 10415.
P. L. Arnold, I. J. Casely, Z. R. Turner, A. I. Germeroth, R. M. Bellabarba, R. P. Tooze, Dalton Trans., 2009, 39, 6808.
P. L. Arnold, Z. R. Turner, R. Bellabarba, R. P. Tooze, J. Am. Chem. Soc., 2010, 132, 4052.
Thanks to: