Organometallics 2010, 29, 5661–5669 5661
DOI: 10.1021/om100557q
Analogies between Metallaboratranes, Triboronates, and Boron Pincer
Ligand Complexes†
Anthony F. Hill,* Stephen B. Lee, James Park, Rong Shang, and Anthony C. Willis
Research School of Chemistry, Institute of Advanced Studies, The Australian National University, Canberra,
Australian Capital Territory 0200, Australia
Received June 5, 2010
The reaction of [RuRCl(CO)(PPh3)2] (R = C6H5, CHdCHPh) with the Yamashita-Nozaki ligand
C6H4{N(CH2PPh2)}2BH (dppBH) results in facile elimination of benzene or styrene and formation of the
ruthenium [PBP]- pincer complex [Ru{κ3B,P,P0-dppB)Cl(CO)(PPh3)] via a stepwise sequence that recalls
the formation of the ruthenaboratrane [Ru(CO)(PPh3){B(mt)3}] (mt = methimazolyl) from [RuRCl-
(CO)(PPh3)2] and Na[HB(mt)3]. This analogy is explored herein, including observations regarding
notionally similar processes for triboronate ligands. Thus, while the major product of the reaction of
[Ru(C6H5)Cl(CO)(PPh3)2] with [nBu4N][B3H8] is the phenylruthenatetraborane [B3H8Ru(C6H5)(CO)-
(PPh3)2], the hydrido complex [B3H8RuH(CO)(PPh3)2] is also obtained, consistent with alcoholic transfer
hydrogenation of the putative complex [B3H7Ru(CO)(PPh3)2].
Introduction
the increased chelate size of, for example, poly(methimazolyl)bo-
rates relative to the more familiar poly(pyrazolyl)borates,5 for
which metallaboratrane formation has never been observed,
presumably due to the geometric strain associated with bicyclo-
[0.2.2] or tricyclo[0.2.2.2] frameworks (Chart 1).
At the time, this chemistry appeared to us novel; however, on
reflection, there have been transformations reported that bear at
least a superficial analogy. The reaction of Vaska’s complex
[IrCl(CO)(PPh3)2] (1) withNa[H2B(mt)2] (mt = methimazolyl)
afforded the first (albeit mer) boron pincer complex, the iri-
daboratrane [IrH(CO)(PPh3){κ3B,S,S0-HB(mt)2}] (2) with a
Metallaboratranes are compounds in which a metal-boron
dative bond is housed within a cage structure, buttressed by two
or three methimazolyl groups. In the intervening decade since the
first report of such a complex,1 the field has matured to the point
that extensive reviews are now available.2 With the exception of
Bourissou’s elegant studies of γ-phosphinoboranes,3 the vast
majority of metallaboratranes arise from the chelate-assisted
B-H activation of the B-H bond of a scorpionate ligand bear-
ing two or three heterocycles that each feature a donor group γto
the boron: i.e. bicyclo[0.3.3] and tricyclo[0.3.3.3] geometries
(Chart 1).4 This is at least in part a geometric consequence of
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† Part of the Dietmar Seyferth Festschrift. Dedicated to Professor Dietmar
Seyferth in recognition of his contributions to chemistry and especially to
Organometallics.
*To whom correspondence should be addressed. E-mail: a.hill@
anu.edu.au.
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r
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