C O M M U N I C A T I O N S
Scheme 2
Figure 2. Thermal ellipsoid plot of 3 (thermal ellipsoids at 50%
probability). Selected bond lengths (Å) and angles (deg): Mo-N(1) 1.7972-
(1), Mo-N(2) 2.2176(15), Mo-N(3) 2.0873(16), Mo-P(1) 2.5385(6), Mo-
P(2) 2.4612(6), Mo-P(3) 2.5204(5).
The deuterium hydride isotopomer of 2 (2a) displays both
coupling with phosphorus (t, 1:2:1, 2JP-H ) 28 Hz) and deuterium
(t, 1:1:1, JH-D ) 15 Hz) (Figure 1). Using the JH-D of 15 Hz in
eq 1 gives a value of 1.17 Å for dHH, which is typical of a stretched-
dihydrogen complex.8(b)
It is possible to correlate the distance between two nuclei to the
relaxation rate due to homonuclear dipole-dipole interactions
between the two nuclei as long as this is the only mechanism of
relaxation. At T1 min the equation for the dipole-dipole relaxation
rate simplifies to that shown in eq 2, and the internuclear distance
(r) can be found.9
We are currently investigating the reactivity of 2 with unsaturated
substrates in catalytic hydrogenation reactions.
1
1
Acknowledgment. J.M.B. thanks the NSF (CHE 0094404), and
K.A.A. thanks the NSF and UF for funding the purchase of X-ray
equipment.
Supporting Information Available: Crystal data, structure refine-
ment, atomic coordinates, bond lengths and angles for 1 and 3, synthesis
and characterization of 1, 2, and 3 (PDF). X-ray crystallographic file
in CIF format. This material is available free of charge via the Internet
(T1 min)-1 ) 77.51 Å6 s-1/r6
(2)
References
A plot of T1 vs temperature for 2 yields a T1 min of 36 ms, which
is normal for a dihydrogen complex. Using eq 2, a value of 1.18 Å
for dHH (r in eq 2) is calculated and this distance is in excellent
(1) Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J.; Wasserman,
H. J. J. Am. Chem. Soc. 1984, 106, 451.
(2) (a) Heinekey, D. M.; Oldham, W. J., Jr. Chem. ReV. 1993, 93, 913. (b)
Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789. (c) Jessop,
P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155. (d) Crabtree, R.
H. Acc. Chem. Res. 1990, 23, 95. (e) Kubas, G. J. J. Organomet. Chem.
2001, 635, 37.
agreement with that value found through application of the
1
measured JH-D
.
(3) (a) Ortiz, C. G.; Abboud, K. A.; Boncella, J. M. Organometallics 1999,
18, 4253. (b) Cameron, T. M.; Ortiz, C. G.; Ghiviriga, I.; Abboud, K. A.;
Boncella, J. M. Organometallics 2001, 20, 2032. (c) Cameron, T. M.;
Abboud, K. A.; Boncella, J. M. Chem. Commun. 2001, 1224. (d) Ortiz,
C. G.; Abboud, K. A.; Cameron, T. M.; Boncella, J. M. Chem. Commun.
2001, 247. (e) Cameron, T. M.; Ortiz, C. G.; Abboud, K. A.; Boncella, J.
M.; Baker, R. T.; Scott, B. L. Chem. Commun. 2000, 573.
(4) Reid, S. M.; Neuner, B.; Schrock, R. R.; Davis, W. M. Organometallics
1998, 17, 4077.
(5) Synthesis, characterization, thermal ellipsoid plot, and the details of the
structure refinement for 1 are included in the Supporting Information.
(6) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.;
Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.
(7) Boncella, J. M.; Wang, S.-Y. S.; VanderLende, D. D. J. Organomet. Chem.
1999, 591, 8.
The tris-PMe3 complex 3 is stable under inert atmosphere and
can be isolated in high yields. An X-ray crystallographic study was
carried out on single crystals of 3 grown from a cold toluene
solution. Complex 3 crystallizes in a monoclinic unit cell, and the
thermal ellipsoid plot of 3 is shown in Figure 2. The Mo-N(1)
bond length of 1.7972(15) Å is typical for a Mo-N triple bond
interaction.3 The metal-amide bond lengths are also within the
expected range.3 The phosphines take up a meridianal bonding motif
in 3, and the Mo-P(1), P(2), and P(3) bond lengths of 2.5385(6),
2.4612(6), and 2.5204(5) Å, respectively, are as expected.
Some reasonable mechanisms for this transformation are shown
in Scheme 2. Route A involves initial silane elimination, forming
an intermediate, 18-electron, bent imido (2b), possibly by way of
a four-centered transition state. This elimination is followed by
hydride migration and coordination of PMe3 to afford 3. During
this transformation the metal center is formally oxidized by two
units. Mechanism B does not involve formal oxidation of the metal
center. Initial H migration to an amide functionality gives the 18-
electron hydrido-amine intermediate 2c. A similar intermediate has
been proposed in a mechanism involving H/D exchange with a
rhenium triamide dihydrogen complex.4 Subsequent silane elimina-
tion from 2c and coordination of PMe3 give 3.10
(8) (a) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J.; Morris, R. H.;
Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J. Am. Chem. Soc. 1996,
118, 5396. Note that a very similar relationship put forth by Heinekey
also appears in the literature and gives essentially the same results as eq
1; Luther, T. A.; Heinekey, D. M. Inorg. Chem. 1998, 37, 127. (b) Law,
J. K.; Mellows, H.; Heinekey, D. M. J. Am. Chem. Soc. 2001, 123, 2085;
and references therein.
(9) Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R.; Halpern, J. J. Am. Chem.
Soc. 1991, 113, 4173; eq 2 is only valid at 500 MHz, and the T1
measurements mentioned herein were carried out at that frequency.
(10) PMe3 does not deprotonate 2 at -20 °C in toluene; therefore, 2 is a weaker
acid than [HPMe3]+ under these conditions; pKRTHF [HPMe3]+ ) 8.7;
Abdur-Rashid, K.; Fong, T. P.; Greaves, B.; Gusev, D. G.; Hinman, J.
G.; Landau, S. E.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2000,
122, 9155.
JA0169365
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