Reactivity of tantalum hydride aryloxide complexes toward organic isocyanide reagents

Article abstract of DOI:10.1021/om950951z

The tantalum monohydride compound [Ta(OC₆H₃Prⁱ₂-2,6) ₂Cl₂(H)(PMe₂Ph)₂] (1) reacts with organic isocyanides RNC to produce the phosphine adduct η²-iminoformyl complexes [Ta(OC₆H₃Prⁱ₂-2,6) ₂Cl₂{HC(PMe₂Ph)NR}] (R = 2,6-diisopropylphenyl (2a), 2,6-dimethylphenyl (2b), tert-butyl (2c)). Compounds 2b,c were only detected spectroscopically as intermediates, while 2a was isolated and reacted with PMe₃ to produce the complex [Ta(OC₆H₃Prⁱ₂-2,6) ₂Cl₂{HC(PMe₃)NC₆H₃Pr ⁱ₂-2,6}] (3), which was structurally characterized. The structure of 3 is best described as trigonal bipyramidal about tantalum with a chloride atom and the phosphine adduct of an η²-iminoformyl group occupying axial sites. Important structural parameters for 3 are Ta-N = 1.956(4), Ta-C = 2.210(5), and N-C = 1.421(7) A?. Compounds 2a and 3 do not react with a further 1 equiv of 2,6-diisopropylphenyl isocyanide. In contrast 2b reacts with 2,6-dimethylphenyl isocyanide to produce the ylide derivative [Ta(OC₆H₃-Prⁱ₂-2,6) ₃Cl₂{RN=CHC(=PMe₂Ph)NR}] (4) (R = C₆H₃Me₂-2,6), while 2c reacts with an additional 2 equiv of Bu^tNC to produce the compound [Ta(OC₆H₃Prⁱ₂-2,6) ₃Cl₂{Bu^tN=CHC-(=C=NBu^t)NBu ^t}] (5). Spectroscopic data on 4 and 5 and a single-crystal X-ray diffraction study of 5 show both molecules contain 2,5-diazacyclopent-2-ene rings with either ylide (4) or keteneimine (5) groups attached to the C-4 position. Addition of Bu^tNC to 2a produces the complex [Ta(OC₆H₃Prⁱ₂-2,6) ₂Cl₂{RN=CHC(=C=NBu^t)NBu^t}] (6) (R = C₆H₃Prⁱ₂-2,6). The tantalum dihydride compound [Ta(OC₆H₃Bu^t₂,-2,6) ₂Cl₂(H)(PMePh₂)] (7) reacts with RNC to produce the monocyclometalated derivatives [Ta(OC₆H₃BU^t-CMe₂CH ₂)(OC₆H₃BU^t₂-2,6)-Cl ₂{N(R)CH₃}] (8) (a, R = C₆H₃Me₂-2,6; b, R = Bu^t), in which a total of three hydride groups have been transferred to the isocyanide substrate to produce the dialkylamido ligand.

Full text of DOI:10.1021/om950951z

3232
Organometallics 1996, 15, 3232-3237
Rea ctivity of Ta n ta lu m Hyd r id e Ar yloxid e Com p lexes
tow a r d Or ga n ic Isocya n id e Rea gen ts
J anet R. Clark, Phillip E. Fanwick, and Ian P. Rothwell*
Department of Chemistry, 1393 Brown Building, Purdue University,
West Lafayette, Indiana 47907-1393
Received December 11, 1995X
The tantalum monohydride compound [Ta(OC6H3Pri2-2,6)2Cl2(H)(PMe2Ph)2] (1) reacts with
organic isocyanides RNC to produce the phosphine adduct 2-iminoformyl complexes
[Ta(OC6H3Pri2-2,6)2Cl2{HC(PMe2Ph)NR}] (R ) 2,6-diisopropylphenyl (2a ), 2,6-dimethylphen-
yl (2b), tert-butyl (2c)). Compounds 2b,c were only detected spectroscopically as intermedi-
ates, while 2a was isolated and reacted with PMe3 to produce the complex [Ta(OC6H3Pri -
2
2,6)2Cl2{HC(PMe3)NC6H3Pri -2,6}] (3), which was structurally characterized. The structure
2
of 3 is best described as trigonal bipyramidal about tantalum with a chloride atom and the
phosphine adduct of an 2-iminoformyl group occupying axial sites. Important structural
parameters for 3 are Ta-N ) 1.956(4), Ta-C ) 2.210(5), and N-C ) 1.421(7) Å. Compounds
2a and 3 do not react with a further 1 equiv of 2,6-diisopropylphenyl isocyanide. In contrast
2b reacts with 2,6-dimethylphenyl isocyanide to produce the ylide derivative [Ta(OC6H3-
Pri -2,6)3Cl2{RNdCHC(dPMe2Ph)NR}] (4) (R ) C6H3Me2-2,6), while 2c reacts with an
2
additional 2 equiv of ButNC to produce the compound [Ta(OC6H3Pri -2,6)3Cl2{ButNdCHC-
2
(dCdNBut)NBut}] (5). Spectroscopic data on 4 and 5 and a single-crystal X-ray diffraction
study of 5 show both molecules contain 2,5-diazacyclopent-2-ene rings with either ylide (4)
or keteneimine (5) groups attached to the C-4 position. Addition of ButNC to 2a produces
the complex [Ta(OC6H3Pri -2,6)2Cl2{RNdCHC(dCdNBut)NBut}] (6) (R ) C6H3Pri -2,6). The
2
2
tantalum dihydride compound [Ta(OC6H3But -2,6)2Cl2(H)(PMePh2)] (7) reacts with RNC to
2
produce the monocyclometalated derivatives [Ta(OC6H3But-CMe2CH2)(OC6H3But -2,6)-
2
Cl2{N(R)CH3}] (8) (a , R ) C6H3Me2-2,6; b, R ) But), in which a total of three hydride groups
have been transferred to the isocyanide substrate to produce the dialkylamido ligand.
In tr od u ction
migratory insertion of 1 equiv of CO.13 Isolated deriva-
tives of these ligands along with related 2-iminoacyl
groups have been shown to undergo a large number of
carbon-carbon bond-forming reactions. In this paper
we report on the reaction of organic isocyanides with
recently isolated hydride-aryloxides of tantalum.14,15
These studies show that the initially formed 2-imino-
formyl complexes can undergo oligomerization reactions
with further equivalents of isocyanide in reaction se-
quences that appear to parallel those previously docu-
mented for carbon monoxide.
The migratory insertion of carbon monoxide and
isoelectronic small molecules into transition metal-
ligand bonds has become an important area of research
in organometallic chemistry.1-5 A particularly signifi-
cant development has been the demonstrated ability of
high-valent early d-block, lanthanide, and actinide
metal hydride, alkyl, and more recently silyl bonds to
not only insert 1 equiv of CO but also to carry out the
oligomerization of multiple equivalents of CO.6-12 Cru-
cial to an understanding of this chemistry is the
structure and reactivity of the 2-formyl, 2-acyl, and
2-silaacyl functional groups formed by the initial
(6) (a) Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.;
Hoffmann, R. J . Am. Chem. Soc. 1985, 107, 4440. (b) Hofmann, P.;
Stauffert, P.; Frede, M.; Tatsumi, K. Chem. Ber. 1989, 122, 1559. (c)
Tatsumi, K.; Nakamura, A.; Hofmann, P.; Hoffmann, R.; Moloy, K.
G.; Marks, T. J . J . Am. Chem. Soc. 1986, 108, 4467.
(7) (a) Fagan, P. J .; Manriquez, J . M.; Marks, T. J .; Day, V. W.;
Vollmer, S. H.; Day, C. S. J . Am. Chem. Soc. 1980, 102, 5393. (b)
Moloy, K. G.; Fagan, P. J .; Manriquez, J . M.; Marks, T. J . J . Am. Chem.
Soc. 1986, 108, 56.
(8) (a) Radu, N. S.; Engeler, M. P.; Gerlach, C. P.; Tilley, T. D.;
Rheingold, A. L. J . Am. Chem. Soc. 1995, 117, 3621. (b) Arnold, J .;
Tilley, T. D.; Rheingold, A. L.; Geib, S. J .; Arif, A. M. J . Am. Chem.
Soc. 1989, 111, 149. (c) Campion, B. K.; Heyn, R. H.; Tilley, T. D.
Organometallics 1993, 12, 2584.
(9) Planalp, R. P.; Andersen, R. A. J . Am. Chem. Soc. 1983, 105,
7774.
(10) Evans, W. J .; Wayda, A. L.; Hunter, W. E.; Atwood, A. L. J .
Chem. Soc., Chem. Commun. 1981, 706.
(11) Bristow, G. S.; Lappert, M. F.; Martin, T. R.; Atwood, J . L.;
Hunter, W. F. J . Chem. Soc., Dalton Trans. 1984, 399.
(12) Porchia, M.; Brianse, N.; Casellato, U.; Ossola, F.; Rossetto, G.;
Zanella, P.; Graziani, R. J . Chem. Soc., Dalton Trans. 1989, 677.
(13) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059.
(14) Parkin, B. C.; Clark, J . R.; Visciglio, V. M.; Fanwick, P. E.;
Rothwell, I. P. Organometallics 1995, 14, 3002.
(1) (a) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry;
J ohn Wiley & Sons: New York, 1988. (b) Collman, J . P.; Hegedus, L.
S.; Norton, J . R.; Finke, R. G. Principles and Applications of Organo-
transition Metal Chemistry; University Science Books: Mill Valley, CA,
1987. (c) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis. The
Applications and Chemistry of Catalysis by Soluble Transition Metal
Complexes, 2nd ed.; Wiley: New York, 1992.
(2) (a) Kahn, B. E.; Rieke, R. D. Chem. Rev. 1988, 88, 733. (b)
Alexander, J . J . In The Chemistry of the Metal-Carbon bond; Hartley,
F. R., Patai, S., Eds.; J ohn Wiley & Sons: Belfast, 1985; Vol. 2, Chapter
5. (c) Wojcicki, A. Adv. Organomet. Chem. 1973, 11, 88. (d) Calder-
azzo, F. Angew. Chem., Int. Ed. Engl. 1977, 16, 299. (e) Treichel, P.
M. Adv. Organomet. Chem. 1973, 11, 21. (f) Singleton, E.; Oosthuizen,
H. E. Adv. Organomet. Chem. 1983, 22, 209.
(3) Wolczanski, P. T.; Bercaw, J . E. Acc. Chem. Res. 1980, 13, 121.
(4) Marks, T. J . In Fundamental and Technological Aspects of
Organo-f-Element Chemistry; Marks, T. J ., Fragala, J . L., Eds.; D.
Reidel: Dordrecht, The Netherlands, 1985.
(5) (a) Erker, G. Acc. Chem. Res. 1984, 17, 103. (b) Erker, G.; Czisch,
P.; Schlund, R.; Angermund, K.; Kru¨ger, C. Angew. Chem., Int. Ed.
Engl. 1986, 25, 364.
(15) Clark, J . R.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Chem.
Commun. 1993, 1233.
S0276-7333(95)00951-4 CCC: $12.00 © 1996 American Chemical Society
+
+

Tantalum Hydride Aryloxide Complexes
Organometallics, Vol. 15, No. 14, 1996 3233
Sch em e 1
F igu r e 1. Molecular structure of [Ta(OC6H3Pri -2,6)2-
2
Cl2{HC(PMe3)NC6H3Pri -2,6}] (3).
2
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for
[Ta (OC6H3P r i2-2,6)2Cl2{HC(P Me3)NC6H3P r i2-2,6}] (3)
Ta-O(30)
Ta-O(40)
Ta-Cl(1)
Ta-Cl(2)
1.896(3)
1.894(3)
2.468(1)
2.354(1)
Ta-N(20)
1.956(4)
2.210(5)
1.421(7)
1.776(5)
Ta-C(10)
N(20)-C(10)
P(10)-C(10)
Cl(1)-Ta-Cl(2)
Cl(1)-Ta-O(30)
Cl(1)-Ta-O(40)
Cl(1)-Ta-N(20)
Cl(1)-Ta-C(10)
Cl(2)-Ta-O(30)
Cl(2)-Ta-O(40)
Cl(2)-Ta-N(20)
Cl(2)-Ta-C(10)
86.33(6) O(30)-Ta-O(40)
141.9(2)
100.0(2)
86.0(2)
100.1(2)
89.5(2)
39.3(2)
80.0(3)
152.3(4)
133.1(3)
60.7(3)
84.1(1)
82.2(1)
O(30)-Ta-N(20)
O(30)-Ta-C(10)
O(40)-Ta-N(20)
O(40)-Ta-C(10)
N(20)-Ta-C(10)
Ta-N(20)-C(10)
Ta-N(20)-C(21)
Ta-C(10)-P(10)
Ta-C(10)-N(20)
169.0(1)
151.7(1)
105.5(1)
108.8(1)
82.8(1)
Resu lts a n d Discu ssion
Syn th esis a n d Sp ectr oscop y of Or ga n om eta llic
P r od u cts. The tantalum monohydride complex [Ta-
(OC6H3Pri -2,6)2Cl2(H)(PMe2Ph)2]14 (1) is only sparingly
2
121.9(1)
soluble in cold hydrocarbon solvents. Suspensions of
colorless 1 in C6D6 solvent will react slowly over hours
with a variety of organic isocyanides to produce much
more soluble organometallic products. Due to its low
solubility, 1 is exposed to large excesses of reagent
throughout the course of these reactions. The progress
of the reactions can be readily monitored by 1H and 31P
NMR spectroscopy. Addition of the sterically very bulky
Ta-O(30)-C(31) 148.7(3)
Ta-O(40)-C(41) 149.9(3)
P(10)-C(10)-N(20) 119.4(4)
Sch em e 2
reagent CNC6H3Pri -2,6 to 1 leads to formation of a
2
single organometallic product [Ta(OC6H3Pri -2,6)2-
2
Cl2{HC(PMe2Ph)NC6H3Pri -2,6}] (2a ) (Scheme 1). In
2
1
the H NMR of 2a a sharp doublet at 3.22 ppm can be
assigned to the iminoformyl proton coupled to the
phosphorus atom with a large, 36 Hz, coupling. The
formulation of 2a as a metal-bound phosphine adduct
of an 2-iminoformyl derivative is ruled out by 13C and
31P NMR data. Previous studies have shown that early
d-block 2-iminoacyl compounds containing aryloxide
ancillary ligation are characterized by a very low field
resonance for the 2-iminoacyl carbon.13 In 2a a doublet
at 51.1 ppm in the proton-decoupled 13C NMR spec-
trum is too high for a simple 2-iminoformyl group. The
large, 71 Hz, coupling to 31P along with the chemical
shift of this phosphorus atom in the 31P NMR spectrum
is consistent with the formulation shown (Scheme 1).
The literature contains examples of related adducts of
acyl and formyl functional groups.8 The addition of
PMe3 to solutions of 2a was found to generate the
corresponding adduct 3 which was structurally charac-
terized (Figure 1, Table 1).
was found to convert to a single organometallic product
formulated as [Ta(OC6H3Pri -2,6)2Cl2{RNdCH-C(PMe2-
2
Ph)NR}] (4) (R ) C6H3Me2-2,6) on the basis of its
spectroscopic data (Scheme 2). The unique TasNdCH
proton which originated from the hydride function is
found as a doublet (5 Hz coupling to 31P) at 6.42 ppm
1
in the H NMR spectrum. In the 13C NMR spectrum
two highly informative doublets are observed at 102.4
(111 Hz) and 148.9 (34.9 Hz). These can be assigned
as the NCdP and NdCH carbons, respectively. Their
coupling constants compare well with those reported for
the compounds Cp*Cl3Ta[OdC(SiMe3)C(dPCy3)O], Cp*2-
ThCl[OdC(CH2But)C(dPPh3)O], and Cp*2ThCl[OdC-
The reaction of 1 with the isocyanide CNC6H3Me2-
2,6 was found (1H and 31P NMR) to initially produce a
mixture of products. One component of this mixture
was identified on the basis of spectroscopic data as the
adduct 2b (Scheme 1). Over time the reaction mixture
+
+

3234 Organometallics, Vol. 15, No. 14, 1996
Clark et al.
Sch em e 3
F igu r e 2. Molecular structure of [Ta(OC6H3Pri -2,6)2Cl2-
2
{ButNdCHC(dCdNBut)NBut}] (5).
Sch em e 4
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for
[Ta (OC6H3P r i2-2,6)2Cl2{Bu tNdCHC(dCdNBu t)NBu t}]
(5)
Ta-O(70)
Ta-O(80)
Ta-Cl(1)
Ta-Cl(2)
Ta-N(2)
Ta-N(5)
1.919(2)
1.854(2)
2.387(1)
2.400(1)
2.271(3)
2.065(3)
N(2)-C(3)
C(3)-C(4)
C(4)-N(5)
C(4)-C(41)
C(41)-N(42)
1.273(5)
1.423(6)
1.401(5)
1.338(6)
1.206(5)
Cl(1)-Ta-Cl(2)
Cl(1)-Ta-O(70)
Cl(1)-Ta-O(80)
Cl(1)-Ta-N(2)
Cl(1)-Ta-N(5)
Cl(2)-Ta-O(70)
Cl(2)-Ta-O(80)
Cl(2)-Ta-N(2)
Cl(2)-Ta-N(5)
Ta-O(70)-C(71)
Ta-O(80)-C(81)
166.67(4)
93.34(8)
94.70(9)
79.18(9)
90.13(9)
87.40(8)
98.56(9)
87.48(9)
87.39(9)
158.8(2)
165.4(2)
O(70)-Ta-O(80)
O(70)-Ta-N(2)
O(70)-Ta-N(5)
O(80)-Ta-N(2)
O(80)-Ta-N(5)
N(2)-Ta-N(5)
Ta-N(2)-C(3)
Ta-N(5)-C(4)
N(2)-C(3)-C(4)
C(3)-C(4)-N(5)
C(4)-C(41)-N(42)
92.6(1)
94.3(1)
171.3(1)
171.0(1)
95.1(1)
78.5(1)
107.9(3)
111.2(2)
121.4(4)
117.9(3)
169.3(4)
data on 8 clearly show the presence of a cyclometalated
2,6-di-tert-butylphenoxide ligand.16 We, therefore, con-
clude that intramolecular CH bond activation gives rise
to the third equivalent of “hydride” needed to convert
the original organic isocyanide into a dialkylamido
function.
(SiR3)C(dPMe2Ph)O].7b,8b The chemical shifts of these
carbons also compare favorably with these other metal
systems when one takes into account that 4 contains
two NR groups instead of O.
Reaction of 1 with ButNC in C6D6 solvent produces
an intermediate adduct complex 2c (identified spectro-
scopically), which is readily converted to a new non-
phosphine-containing organometallic product 5 (Scheme
2). A single-crystal X-ray diffraction analysis of 5
(Figure 2, Table 2) shows it to contain 3 equiv of But-
NC coupled by the single Ta-H functional group to
produce a diazametallacycle with an exocyclic ketene-
imine group. This compound is related to an oxa-aza
Str u ctu r a l Stu d ies. The solid-state structure of 3
(Figure 1, Table 1) is best described as trigonal bipy-
ramidal with a chloride atom and the phosphine adduct
of an iminoformyl group occupying axial sites. The
TaNC unit is oriented so that the NC vector lies
coplanar with the equatorial Ta-Cl bond. The most
interesting features of the structure of 3 relates to the
structural parameters of the iminoformyl group. The
literature presently contains no analogous phosphine
adduct of an 2-iminoformyl. There is, however, a
related phosphine adduct of a silaacyl, [Cp*TaCl3{OC-
(SiMe3)(PEt3)}], studied by Tilley et al.8b,17 The Ta-
metallacyclic
analogue
[Cp*2ThCl{OC(CH2But)-
C(dCdNR)NR}] and the dioxa derivative [Cp*2ThCl-
{OC(SiR3)C(dCdNR)O}].7b,8a
A direct analogue of 5 was obtained by addition of
ButNC to the iminoformyl complex 2a . In this case
incorporation of a further 2 equiv of isocyanide occurs
with displacement of PMe2Ph and formation of the
N(20) distance of 1.956(4) Å in 3 is much shorter than
2
the Ta-N distances of 2.15(5) and 2.165(5) Å in the
-
iminoacyl compound [Ta(OC6H3Me2-2,6)2(Me)( 2-MeC-
NAr)2] (Ar ) C6H3Me2-2,6).18 In contrast the Ta-C(10)
distance of 2.210(5) Å in 3 is slightly longer than the
Ta-C distances of 2.187(7) and 2.200(6) Å in the bis-
organometallic
compound
[Ta(OC6H3Pri -2,6)2Cl-
2
{ArNdCHC(dCdNBut)NBut}] (6) (Scheme 3; Ar )
C6H3Pri -2,6). As expected, 6 has many spectroscopic
(
2-iminoacyl). The C-N distance in 3 of 1.421(7) Å is
2
similarities with 5.
The six-coordinate dihydride complex [Ta(OC6H3But -
2
(16) Rothwell, I. P. Acc. Chem. Res. 1988, 21, 153.
2,6)2Cl(H)2(PMePh2)] (7) will also react with organic
isocyanides. In this case, however, only 1 equiv of RNC
is incorporated to produce the corresponding methyl,
alkyl amido complexes 8 (Scheme 4). The spectroscopic
(17) Rheingold, A. L. Acta Crystallogr. 1990, C46, 2374.
(18) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger,
L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.;
Huffman, J . C.; Streib, W. E.; Wang, R. J . Am. Chem. Soc. 1987, 109,
390.
+
+

Tantalum Hydride Aryloxide Complexes
Organometallics, Vol. 15, No. 14, 1996 3235
Sch em e 5
much longer than the 1.28(8) and 1.286(8) Å distances
found for the 2-iminoacyl groups and is very close to
that expected for a carbon-carbon single bond.
derivatives of high-valent d-block, lanthanide and ac-
tinide metals have characterized the carbon center as
being electrophilic in nature.6,13 Many possible reso-
nance pictures for these functional groups have been
proposed (e.g. [A] in Scheme 5). The structural studies
of 2-iminoacyl groups do show significant shortening
of the metal-nitrogen bond below that expected for a
simple dative interaction, but C-N distances clearly fall
in the range expected for double bonds.18 The phosphine
adducts 2 obtained in this study are consistent with the
carbon atom of the 2-iminoformyl being highly electro-
philic. In the case of the bulky nitrogen substituent 2,6-
diisopropylphenyl (2a ) the phosphine ligand has been
shown to bind reversibly by exchange with PMe3 to
produce 3 (Figure 1).
The solid-state structure of 5 (Figure 2, Table 2)
shows a six-coordinate tantalum metal center with
mutually trans chloride groups and cis aryloxide ligands.
The geometry about tantalum is distorted, with both
chloride ligands bent toward the atom N(2). This
nitrogen atom is (vide infra) a datively bound imine
function. Distortions of covalently bound ligands toward
dative bonds is a characteristic feature of six-coordinate,
d0-metal complexes of this type, and a theoretical
analysis has been carried out.19 The most interesting
structural features of 5 concern the parameters for the
metallacyclic ring. Analysis of bond distances is entirely
consistent with a 2,5-diazatantalacyclopent-2-ene ring
as shown (Scheme 2). The Ta-N(2) distance of
2.271(3) Å is much longer than the Ta-N(5) distance
of 2.065(3) Å. The former distance is comparable to the
The metallacyclic compounds obtained in this study
can be envisaged as arising via two alternative path-
ways. Dissociation of phosphine from the adduct 2 leads
to an 2-iminoformyl complex [A], which can coordinate
a second 1 equiv of isocyanide. This coordination can
occur either at the electrophilic carbon or the electron-
Ta-py distances of 2.315(6) Å in [Ta(OC6H3Pri -2,6)2-
2
Cl3(py)],19 while the latter is closer to distances of
dialkylamido groups bound to tantalum; cf. distances
of 1.963(5) and 1.954(5) Å in [TaCl3(NMe2)2(HNMe2)].20
Mech a n istic Con sid er a tion s. The reaction of or-
ganic isocyanides with the tantalum hydride aryloxides
1 and 7 leads to a diverse series of organometallic
compounds. The product molecules can, however, be
accommodated into a unified reaction scheme in which
the pivotal intermediate is the initial 2-iminoformyl
derivative. Previous synthetic and theoretical studies
on the chemistry of 2-acyl, 2-iminoacyl, and related
deficient metal center. The former would lead to an
2
amido keteneimine [B] while the latter generates an
-
iminoacyl [C] containing an imine group attached to the
R-carbon. This latter reaction is the sequential migra-
tory insertion of two isocyanide molecules into the
tantalum-hydride bond. There is at present no prece-
dence for the formation of compounds such as [C].
There is, however, excellent precedence for the forma-
tion of ketene and keteneimine functions by addition of
CO or RNC to 2-acyl groups.7,8 The observed products
can be generated from [C] by nucleophilic attack at the
iminoacyl carbon either by phosphine, to produce [D],
or by isocyanide, to produce [E] (Scheme 5). Although
many ketene and keteneimine complexes had previously
(19) Clark, J . R.; Eisenstein, O.; Rothwell, I. P. Results to be
published.
(20) Chisholm, M. H.; Huffman, J . C.; Tan, L.-S. Inorg. Chem. 1981,
20, 1859.
+
+

3236 Organometallics, Vol. 15, No. 14, 1996
Clark et al.
stored under dry nitrogen. 2,6-Diisopropylphenyl isocyanide
was prepared by reported procedures. 2,6-Dimethylphenyl
isocyanide was purchased from Fluka Chemical Co. Phos-
phines and tert-butyl isocyanide were all purchased from
Strem Chemical Co. and were dried over 3 Å molecular sieves
prior to use. [Ta(OC6H3Pri2-2,6)2(Cl)2H(PMe2Ph)2] (1) and [Ta-
Sch em e 6
(OC6H3But -2,6)2Cl(H)2(PMePh2)] (7) were prepared by re-
2
1
ported procedures.14 The H, 13C, and 31P NMR spectra were
recorded on a Varian Associates Gemini 200 and a General
Electric QE-300 spectrometer and were referenced to protio
impurities of commercial benzene-d6.
[Ta(OC6H3P r i -2,6)2Cl2{HC(P Me2P h )NC6H3P r i -2,6}] (2a).
2
2
To a suspension of [Ta(OC6H3Pri2-2,6)2Cl2(H)(PMe2Ph)2] (1) (0.5
g, 0.57 mmol) in benzene (5 mL) was added 2,6-diisopropyl-
phenyl isocyanide (0.13 g, 0.68 mmol). The resulting red
solution was stirred for 20 h. Slow cooling of a warmed toluene
solution yielded product as colorless crystals, which were
washed in hexane and dried in vacuo with high yield. 1H NMR
(C6D6, 30 °C, ): 6.67-7.14 (m, 14H, aromatics); 4.07 (septet,
1H, CHMe); 3.87 (septet, 4H, CHMe); 3.22 (d, 1H, 2-(C6H3-
Pri2-2,6)NCH), 2J (31P-1H) ) 35.7 Hz; 3.11 (septet, 1H, CHMe);
1.64 (d, 3H, CHMe); 1.57 (d, 3H, CHMe); 1.40 (d, 12H, CHMe);
1.33 (d, 12H, CHMe); 1.23 (d, 3H, CHMe); 1.14 (d, 3H, CHMe);
Sch em e 7
0.89 (d, 6H, P-Me), 2J (31P-1H) ) 7.0 Hz. 13C NMR (C6D6, 30
2
°C, ): 158.2 (TaOC); 120.5-150.0 (aromatics); 51.1 (
-
ArNCH), 1J (13C-31P) ) 71.1 Hz; 9.29-30.2 (aliphatics). 31P
NMR (C6D6, 30 °C):
25.6.
[Ta(OC6H3P r i -2,6)2Cl2{HC(P Me2P h )NC6H3Me2-2,6}] (2b).
2
This compound was detected by 1H and 31P NMR in the
reaction mixture of 3. 1H NMR (C6D6, 30 °C): 3.37 (d, 1H,
2-(C6H3Me2-2,6)NCH), 2J (31P-1H) ) 34.0 Hz. 31P NMR (C6D6,
30 °C):
26.1.
[Ta (OC6H3P r i2-2,6)2Cl2{HC(P Me2P h )NBu t}] (2c). This
compound was detected by 1H and 31P NMR in the reaction
mixture of 4. 1H NMR (C6D6, 30 °C):
2.60 (d, 1H, 2-But-
NCH), J (31P-1H) ) 42.0 Hz. 31P NMR (C6D6, 30 °C): 22.2.
2
[Ta(OC6H3P r i -2,6)2Cl2{HC(P Me3)NC6H3P r i -2,6}] (3). To
2
2
a suspension of 1a (0.5 g, 0.57 mmol) in benzene (5 mL) was
added trimethylphosphine (0.85 mmol). The resulting solution
was allowed to stand for 10 h to yield the crystalline product.
The colorless crystals were washed with hexane and dried in
vacuo; yield 0.4 g (81.2%). 1H NMR (C6D6, 30 °C, ): 6.92-
7.43 (m, 9H, aromatics); 4.10 (septet, 1H, CHMe); 3.83 (septet,
4H, CHMe); 3.05 (septet, 1H, CHMe); 2.80 (d, 1H, 2-(C6H3-
been isolated, direct evidence for their conversion to
metallacycles such as [D] and [E] had been absent until
very recently. In an important study Tilley et al. have
shown that addition of PR3 or RNC to a metallaoxy-
ketene generates just such products (Scheme 6).8a On
the basis of this work, we, therefore, now propose that
the products obtained in this study originate from an
undetected intermediate amido keteneimine [B] al-
though we cannot conclusively rule out intermediates
such as [C] on the basis of experiments in hand.
The cyclometalated compounds 8 (Scheme 4) arise
from the addition of isocyanide to the dihydride 7.
Previous work has shown that 2-iminoacyl ligands can
be converted to 2-imine groups by migration of a second
alkyl substituent from the metal to the R-carbon. In
the case of the formation of 8, intramolecular CH bond
activation in which the azametallacyclopropane is opened
up leads to the final dialkylamide product (Scheme 7).
The ligand 2,6-di-tert-butylphenoxide has been shown
to undergo facile cyclometalation at early d-block metal
centers with a variety of activating functional groups.16
Pri -2,6)NCH), 2J (31P-1H) ) 40.0 Hz; 1.48 (d, 6H, CHMe); 1.36
2
(d, 12H, CHMe); 1.32 (d, 12H, CHMe); 1.18 (d, 6H, CHMe);
2
1.08 (d, 9H, P-Me), J (31P-1H) ) 3.3 Hz. 31P NMR (C6D6, 30
°C):
23.35.
[Ta(OC6H3P r i -2,6)2Cl2{(C6H3Me2-2,6)NdCHC(P Me2P h )N-
2
(C6H3Me2-2,6)}] (4). To a suspension of [Ta(OC6H3Pri -2,6)2-
2
Cl2(H)(PMe2Ph)2] (0.5 g, 0.57 mmol) in benzene (5 mL) was
added 2,6-dimethylphenyl isocyanide (0.15 g, 1.13 mmol). The
resulting dark red solution was stirred for 20 h. Removal of
benzene solvent led to the crude product as a red-brown solid,
which was washed with hexane and dried in vacuo to yield
0.56 g (98%). Anal. Calcd for C50H64N2PO2Cl2Ta: C, 59.62;
H, 6.41; N, 2.78; Cl, 6.95; P, 3.08. Found: C, 60.02; H, 6.70;
N, 2.99; Cl, 6.66; P, 2.72. 1H NMR (C6D6, 30 °C, ): 6.55-
2
7.25 (m, 17H, aromatics); 6.42 (d, 1H, HCdN), J (31P-1H) )
4.8 Hz; 4.05 (septet, 2H, CHMe); 3.80 (septet, 2H, CHMe); 3.01
(s, 3H, CMe); 2.45 (s, 3H, CMe); 1.19 (d, 12H, CHMe); 1.15 (d,
2
12H, CHMe); 0.59 (d, 6H, P-Me), J (31P-1H) ) 13.2 Hz. 13C
NMR (C6D6, 30 °C, ): 157.5 (TaOC); 153.5 (TaOC); 148.9
(NdCH), 2J (13C-31P) ) 34.9 Hz; 122.5-138.2 (aromatics);
102.4 (NCdP), 1J (13C-31P) ) 111 Hz; 14.37-26.36 (aliphatics);
11.28 (P-Me), 1J (13C-31P) ) 59.2 Hz. 31P NMR (C6D6, 30 °C);
3.43.
Exp er im en ta l Section
[Ta(OC6H3P r i -2,6)2Cl2{Bu tNdCHC(dCdNBu t)NBu t}] (5).
2
All operations were carried out under
a
dry nitrogen
To a suspension of [Ta(OC6H3Pri -2,6)2Cl2(H)(PMe2Ph)2] (0.5
2
atmosphere or in vacuo either in a Vacuum Atmosphere Dri-
Lab or by standard Schlenk techniques. Hydrocarbon solvents
were dried by distillation from sodium/benzophenone and
g, 0.57 mmol) in benzene (5 mL) was added tert-butyl isocya-
nide (0.09 g, 1.13 mmol). The dark red solution was stirred
for 20 h. Slow cooling of a warmed hexane solution yielded
+
+

Tantalum Hydride Aryloxide Complexes
Organometallics, Vol. 15, No. 14, 1996 3237
red crystals, which were washed in hexane and dried in vacuo
with high yield. Anal. Calcd for C39H62N3O2Cl2Ta: C, 54.67;
H, 7.29; N, 4.90; Cl, 8.28. Found: C, 55.05; H, 7.59; N, 5.29;
Cl, 8.37. 1H NMR (C6D6, 30 °C, ): 8.05 (s, 1H, NdCH); 7.17-
6.90 (m, 6H, aromatics); 4.47 (septet, 2H, CHMe); 4.14 (septet,
2H, CHMe); 1.63 (s, 9H, CMe); 1.38 (d, 12H, CHMe); 1.30 (s,
9H, CMe); 1.15 (s, 9H, CMe); 1.14 (d, 12H, CHMe). 13C NMR
(C6D6, 30 °C, ): 180.1 (CdCdN); 166.7 (NdCH); 156.7
(TaOC); 123.9-141.4 (aromatics); 95.6 (CdCdN); 64.4, 63.7,
63.3 (NCMe); 31.2, 30.4, 29.6 (NCMe); 24.4-26.6 (aliphatics).
[Ta(OC6H3P r i -2,6)2Cl2{(C6H3P r i -2,6)NdCHC(dCdNBu t)-
3.37 (d, 1H), 2.73 [d, 1H, Ta-CH2, 2J (1H-1H) ) 15.8 Hz], 2.61
(s, 3H, CMe); 2.52 (s, 3H, CMe); 1.60 (m, 9H, CMe3); 1.39 (s,
3H, CMe2); 1.37 (s, 3H, CMe2); 1.30 (m, 9H, CMe3); 1.25 (s,
9H, CMe3). 13C NMR (C6D6, 30 °C, ): 163.3 (TaOC); 156.4
(TaOC); 148.8 (NC ipso); 142.3 (C-CMe2); 122.5-137.6 (aro-
matics); 94.8 (TaCH2); 45.9 (NCH3); 32.0, 31.3 (TaCH2CMe3);
17.3-39.4 (aliphatics).
[ T a ( O C 6 H 3 B u t 2 -2 , 6 ) ( O C 6 H 3 B u t C M e 2 C H 2 ) C l {N -
(Bu t)CH3}] (8b). To a suspension of [Ta(OC6H3But -2,6)2Cl-
2
(H)2(PMePh2)] (0.1 g, 0.12 mmol) in benzene-d6 (1 mL) was
added tert-butyl isocyanide (0.03 g, 0.35 mmol). A yellow
solution was observed. The product was only spectroscopically
characterized. 1H NMR (C6D6, 30 °C, ): 6.78-7.29 (m, 6H,
aromatics); 3.35 (s, 3H, NCH3); 3.02 (d, 1H), 2.66 [d, 1H, Ta-
CH2, 2J (1H-1H) ) 16.6 Hz], 1.52 (m, 9H, N-tBu); 1.44 (s, 18H,
CMe3); 1.40 (s, 3H, CMe2); 1.36 (s, 3H, CMe2); 1.35 (m, 9H,
CMe3). 13C NMR (C6D6, 30 °C, ): 162.5 (TaOC); 158.2 (TaOC);
143.0 (C-CMe2); 123.0-139.8 (aromatics); 101.4 (TaCH2); 61.5
(NCMe3); 36.2 (NCH3); 31.9, 30.1 (TaCH2CMe2); 18.5-40.7
(aliphatics).
2
2
NBu t}] (6). To a concentrated solution of 2a (0.1 g, 0.11 mmol)
in benzene-d6 (1 mL) was added tert-butyl isocyanide (0.03 g,
0.35 mmol). The product was only spectroscopically character-
ized. 1H NMR (C6D6, 30 °C, ): 7.95 (s, 1H, NdCH); 6.91-
7.17 (m, 9H, aromatics); 4.45 (septet, br, 2H, CHMe); 4.17
(septet, br, 2H, CHMe); 3.03 (septet, 2H, CHMe); 1.70 (s, 9H,
CMe); 1.44 (m, br, 12H, CHMe); 1.17 (d, 6H, CHMe); 1.07 (d,
6H, CHMe); 1.06 (s, 9H, CMe). 13C NMR (C6D6, 30 °C, ):
174.6 (NdCH); 156.9 (CdCdN); 148.2 (TaOC); 123.4-131.2
(aromatics); 96.1 (CdCdN); 65.1, 63.4, (NCMe); 30.9, 30.5
(NCMe); 23.1-29.8 (aliphatics).
Ack n ow led gm en t. We thank the Department of
Energy for financial support of this research.
[Ta (OC6H3Bu t2-2,6)(OC6H3Bu tCMe2CH2)Cl{N(C6H3Me2-
2,6)CH3}] (8a ). To a suspension of [Ta(OC6H3But -2,6)2Cl-
2
(H)2 (PMePh2)] (7) (0.5 g, 0.65 mmol) in benzene-d6 (5 mL),
was added 2,6-dimethylphenyl isocyanide (0.1 g, 0.78 mmol).
The resulting red solution was stirred for 18 h. Removal of
the benzene solvent led to the crude product as a red-brown
solid. Layering a concentrated benzene solution with hexane
yielded product as red crystals, which were washed with
hexane and dried in vacuo with high yield. 1H NMR (C6D6,
30 °C, ): 6.58-7.25 (m, 9H, aromatics); 3.79 (s, 3H, NCH3);
Su p p or tin g In for m a tion Ava ila ble: Text describing the
experimental procedures for X-ray diffraction studies and
tables of positional and thermal parameters, bond distances
and angles, and data collection parameters for 3 and 5 (42
pages). Ordering information is given on any current mast-
head page.
OM950951Z
+
+