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40812-B3
Solid-State and Solution Behavior of Lanthanide Scorpionates and Porphyrinoids

Gregory M. Ferrence, Illinois State University

<p>We have been examining the reaction chemistry displayed by the divalent lanthanide complex [(Tp^{<i>t</i>Bu,Me})Yb(mu₂-H)]₂, <b>1</b>, where Tp^{<i>t</i>Bu,Me} equals tris(3-<i>tert</i>-butyl-5-methylpyrazolyl)borate.  This (Tp^{<i>t</i>Bu,Me}) scorpionate ligand is particularly well suited for stabilizing low coordinate divalent lanthanide complexes.  Hydride <b>1</b> reacts with various protic substrates such as amines, terminal alkynes, and alcohols to form the corresponding lanthanide- amides, alkynides, and alkyl- or aryl- oxides. </p>

            <p>Prior to this award, we and our collaborators reported preparation and structure of the ytterbium aryloxide, (Tp^{<i>t</i>Bu,Me})Yb(O-{2,6-(Me) ₂C₆H₂-4-Me}) and a THF solvated variant, (Tp^{<i>t</i>Bu,Me})Yb(O-{2,6-(Me)₂C₆H₂-4-Me})(THF).  During the tenure of this award, several series of ytterbium(II) aryloxides were prepared.  Series included (Tp^{<i>t</i>Bu,Me})Yb(OAr) (Ar = 2,6-(Me)₂C₆H₂-4-X) (X = H, Cl, Br, and I),  (Tp^{<i>t</i>Bu,Me})Yb(OAr) (Ar = 2,6-( tBu)₂C₆H₂-4-X) (X = CH₃, ^<i>t</i>Bu), (Tp^{<i>t</i>Bu,Me})Yb(O-C₆H₄-4-X ) (X = H, F, Cl, Br, I, CF₃, OMe and N₂), and the THF solvated derivatives. </p>

            <p>We examined preparation of a series of <i>para</i>-substituted phenols having protons rather than alkyl groups in the 2 and 6 positions to study the correlation between the electronics of the aryloxide and the Yb-O-C bond angle.  At this point we have found that the (Tp^{<i>t</i>Bu,Me})Yb(p-OC₆H₄X)(THF) complexes may be prepared from (Tp^{<i>t</i>Bu,Me})Yb(CH₂SiMe₃)(THF); however, products of the less bulky (Tp^{<i>t</i>Bu,Me})Yb(<i>p</i>-OC₆H₄X) complexes formed from <b>1</b> have so far contained significant to substantial amounts of the common degradation product, (Tp^{<i>t</i>Bu,Me})</sub>2</sub>Yb.  In contrast we found that use of bulky phenols allowed preparation of  (Tp^{<i>t</i>Bu,Me})Yb(O-{2,6-(tBu) ₂-C₆H₂-4-X}) (X = CH₃, ^<i>t</i>Bu) from <b>1</b>; however, dissolution of these products in THF or reaction of (Tp^{<i>t</i>Bu,Me})Yb(CH₂SiMe₃)(THF) with bulky phenols has led to only decomposition products.  This study very nicely illustrates the profound effects sterics plays on the stability of these complexes. </p>

            <p>During the final year of this award, we examined the reactivity of <b>1</b> with pyrazoles.  Reaction of <b>1</b> with ( Hpz^<i>t</i>Me2) appears to cleanly yield (Tp^{<i>t</i>Bu,Me})Yb(pz^<i>t</i>Me2); although, without an X-ray structure at hand, we have yet to determine the exact binding mode of the pyrazolide.  We examined the reactivity of (Tp^{<i>t</i>Bu,Me})Yb(pz^<i>t</i>Me2) with stoichiometric and excess phenols and we examined the reactivity of (Tp^{<i>t</i>Bu,Me})Yb(O-{2,6-(Me)₂C₆H₂-4-Me})(THF) with stoichiometric and excess dimethylpyrzaole.  NMR evidence suggests the formation of (Tp^{<i>t</i>Bu,Me})Yb(O-{2,4,6-(Me)₃C₆H₂})( Hpz^<i>t</i>Me2) and perhaps (Tp^{<i>t</i>Bu,Me})Yb(O-{2,4,6-(Me)₃C₆H₂})( Hpz^<i>t</i>Me2)₂; however, solutions appear to contain equilibrating mixtures of products.  Further investigation, beyond this award, will be required to work out this chemistry. </p>

<p>Another objective sought, in part, under this award’s funding was establishment of the first lanthanide complexes of N-confused-porphyrins and azuliporphyrins.  The PI has, in collaboration with colleague and Distinguished Professor T.D. Lash, published a series of structures of novel porphyrinoids and porphyrinoid metal complexes.  Lash is an expert in the organic synthesis of novel porphyrinoids, and the PI routinely handles the crystallographic analysis of Lash’s porphyrinoids.  This has provided the PI an opportunity to learn much about synthetic aspects of such compounds as well as contribute to important scholarly works.  As appropriate, time and effort from this award spent on these activities have led to ACS-PRF acknowledgement on several of these manuscripts.  Even with the insight gained and the significant effort students have put into preparing lanthanide complexes of N-confused-porphyrins and azuliporphyrins, characterizable lanthanide containing products have thus far eluded us.  Details may be found in prior annual reports for this award.  With what has been learned from the research associated with this award, several viable, albeit technically challenging routes to the desired complex have been identified; however, carrying out these new procedures must await future funding. </p>

<p>With our successful examinations of the reaction chemistry displayed by the divalent lanthanide complex (Tp^{<i>t</i>Bu,Me})Yb(mu₂-H)] ₂ we began development of a synthesis for a closely related ligand.  During 2007, in collaboration with Professor L. Papish, then at Salisbury Sate University, we reported the synthesis of the 3-<i>tert</i>-butyl-5-methyl(1,2,4-triazole) as well as the preparation and characterization of several tris(3-<i>tert</i>-butyl-5-methyl(1,2,4-triazolyl)borate, Ttz^{<i>t</i>Bu,Me}, metal complexes.  Few tristriazolylborate metal complexes have been reported in the literature and none using the bulky Ttz^{<i>t</i>Bu,Me} ligand. </p>

<p>During 2007, one PRF funded undergraduate researcher examined the coordination chemistry of 3-<i>tert</i>-butyl-5-methyl(1,2,4-triazole), Htz^{<i>t</i>Bu,Me}, and comparing it to the related 3-<i>tert</i>-butyl-5-methylpyrazole, Hpz^{<i>t</i>Bu,Me}.  Reaction of [Cp*RuCl] ₄ with Hpz^{<i>t</i>Bu,Me} leads to clean formation of (eta⁵-Cp*)Ru(eta⁵-pz^{<i>t</i>Bu,Me}), whereas substitution with Htz^{<i>t</i>Bu,Me} forms a complex mixture.  Reaction of two equivalents of Hpz^{<i>t</i>Bu,Me} with PdCl₂ cleanly forms Hpz^{<i>t</i>Bu,Me}PdCl₂, which afforded X-ray quality crystals upon crystallization from chloroform-hexanes.  In contrast, reaction of two equivalents of Htz^{<i>t</i>Bu,Me} with PdCl₂ affords only an insoluble off-white solid.  </p>

<p>It appears that tz^{<i>t</i>Bu,Me} will have limited utility as a simple ligand; however, as a tristriazolylborate ligand, it may be quite useful. Eventually we intend to examine the feasibility of preparation of  (Ttz^{<i>t</i>Bu,Me})Yb(mu₂-H)]₂; however, attempts to prepare this molecule remain a future as undergraduate researchers new to this project spent the final year of this award learning to prepare the Htz^{<i>t</i>Bu,Me} and we still working to isolate quality K(Ttz^{<i>t</i>Bu,Me}) at the time this award expired. </p>

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