C O M M U N I C A T I O N S
The investigation of the mechanism was performed by locating
a transition-state structure on the potential hypersurface and also
by taking a closer look at the possible alternative mechanism. The
possible routes involving a two-step mechanism start with either
hydrogen or water formation. Assuming that H2 elimination is the
first step of the reaction does not lead to the desired compound
due to the rearrangement taking place in the Ph-B-OH unit (Figure
S1, see Supporting Information). However the condensation as the
first step looks quite promising as the transition state diagram
indicates (Figure S2, see Supporting Information). But trying to
reach the target molecule from this transition state is impossible
due to the fact that the bond formation between aluminum and
oxygen does not take place. Having ruled out this possible
mechanistic explanation, it is quite reasonable that the calculated
transition state shown in Figure S3 (see Supporting Information)
is the crucial step in this reaction. The calculations indicate that
the reason for the formation of the transition structures A and B
proposed here is valid.
Figure 1. Molecular structure of 3; thermal ellipsoids set at 50% probability.
All hydrogen atoms and the toluene molecule are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: N(1)-Al(1) 1.877(6), N(2)-
Al(1) 1.872(6), Al(1)-O(2) 1.754(5), Al(1)-O(3) 1.745(5), O(2)-B(2)
1.326(10), O(3)-B(1) 1.339(10), B(2)-O(1) 1.415(11), O(1)-B(1) 1.401-
(10), B(2)-C(21) 1.574(11), B(1)-C(11) 1.559(11); N(2)-Al(1)-N(1)
98.8(3), O(2)-Al(1)-O(3) 104.7(3), O(3)-Al(1)-N(2) 113.2(3), O(2)-
Al(1)-N(2) 111.9(3), O(3)-Al(1)-N(1) 115.0(3), O(2)-Al(1)-N(1) 113.6-
(3), O(3)-B(1)-O(1) 122.4(7), B(2)-O(2)-Al(1) 121.7(5), O(2)-B(2)-
O(1) 122.5(8), B(1)-O(3)-Al(1) 121.7(5).
In summary the different reactions between PhB(OH)2 with LAl-
(I) or LAlH2(III) result in the same compound 3 in high yields.
Acknowledgment. This work was supported by the Fonds der
Chemischen Industrie and the Go¨ttinger Akademie der Wissen-
schaften.
Table 1. Calculated Bond Lengths and Angles
distance
[Å]
angle
[deg]
Supporting Information Available: Figures S1, S2, and S3;
Experimental Section, including detailed synthetic procedures and
analytical and spectral characterization data; CIF data for 3; complete
ref 14. This material is available free of charge via the Internet at http://
pubs.acs.org.
Al(1)-O(2)
Al(1)-O(3)
B(2)-O(1)
B(2)-O(2)
1.7901
1.7896
1.4137
1.3749
O(2)-Al(1)-O(3)
O(3)-B(1)-O(1)
O(2)-B(2)-O(1)
N(1)-Al(1)-N(2)
100.81
119.65
119.37
98.89
that the Al-O bond lengths in 3 increase when compared to those
in LAl(OH)2 and (LAl)2O3AlMe (1.708-1.726 Å).11 The wider
O-B-O bond angles (122.4(7)°, 122.5(8)°) in comparison to the
O-Al-O (104.7(3)°) are a consequence of the lower coordination
number at boron compared to that at aluminum.
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