Chemical behaviour of alkyl imido cyclopentadienyl niobium and tantalum(V) complexes in insertion processes. X-ray crystal structures of [MCpCl(NAr){η2-C(Me)=NAr}] (Ar=2,6-Me2C6H3; M=Nb, Cp=η5-C5H4SiMe3; M=Ta, Cp=η5-C5Me5).

Article abstract of DOI:10.1016/S0022-328X(99)00566-5

Pure imido η²-iminoacyl derivatives [MCpX(NAr){η²-C(R)=NAr}] (Ar=2,6-Me₂C₆H₃; M=Nb, Cp=η⁵-C₅H₄SiMe₃=Cp′, X=Cl, R=Me, 1; X=Me, R=NMe₂, 2; Me, 3; X=R=CH₂SiMe₃, 4; CH₂CMe₃, 5; CH₂Ph, 6; M=Ta, Cp=η⁵-C₅Me₅=Cp*, X=Cl, R=Me, 7; CH₂SiMe₃, 8; CH₂CMe₂Ph, 9; CH₂CMe₃, 10; CH₂C₆H₅, 11; 2-(CH₂NMe₂)C₆H₄, 12; NMe₂, 13; X=R=CH₂SiMe₃, 14; CH₂CMe₂Ph, 15; CH₂CMe₃, 16; CH₂C₆H₅, 17; C₆H₅, 18) can be prepared by reaction of chloro alkyl or dialkyl imido complexes MCpXR(NAr) with 1 equivalent of 2,6-Me₂C₆H₃NC. Reaction of alkyl methyl imido complexes TaCp*RMe(NAr) with 1 equivalent of isocyanide 2,6-Me₂C₆H₃NC takes place with migration of alkyl or methyl group, leading to the formation of a mixture of methyl η²-alkyliminoacyl [TaCp*Me(NAr){η²-C(R)=NAr}] (Ar=2,6-Me₂C₆H₃; R=CH₂SiMe₃, 19; CH₂Ph, 21; CH₂CMe₂Ph, 23; CH₂CMe₃, 25; C₆H₅, 27; 2-(CH₂NMe₂)C₆H₄, 29; NMe₂, 30) and alkyl η²-methyliminoacyl [TaCp*R(NAr){η²-C(Me)=NAr}] (Ar=2,6-Me₂C₆H₃; R=CH₂SiMe₃, 20; CH₂Ph, 22; CH₂CMe₂Ph, 24; CH₂CMe₃, 26; C₆H₅, 28) complexes. Alkyl imido derivatives also react with CO to give alkyl η²-acyl [TaCp*X(NAr){η²-C(R)=O}] (Ar=2,6-Me₂C₆H₃; X=R=CH₂SiMe₃, 31; CH₂CMe₂Ph, 32; CH₂CMe₃, 33; CH₂Ph, 34), chloro η²-acyl (X=Cl, R=CH₂CMe₂Ph, 35; NMe₂, 36) and methyl η²-acyl (X=Me, R=CH₂CMe₂Ph, 37; CH₂CMe₃, 38) complexes. Dinuclear ene diolate complexes [{TaCp*X(NAr)}₂{μ-η²-OC(R)=C(R)O}] (Ar=2,6-Me₂C₆H₃; X=Cl, R=CH₂CMe₃, 39; X=Me, R=2-(CH₂NMe₂)C₆H₄, 40) are formed by reaction of the chloro and methyl alkyl imido derivatives with carbon monoxide, whereas using [TaCp*XR(NAr)] (Ar=2,6-Me₂C₆H₃; X=Cl, R=CH₂CMe₃; X=R=Ph) a different sequence of reactions takes place leading finally to oxo η²-iminoacyl complexes [TaCp*X(O){η²-C(R)=NAr}] (X=Cl, R=CH₂CMe₃, 41; X=R=Ph, 42). All compounds were characterised by NMR (¹H, ¹³C) spectroscopy and IR measurements. The molecular structures of 1, 7 and 37 were studied by X-ray diffraction methods and are discussed.

Full text of DOI:10.1016/S0022-328X(99)00566-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 595 (2000) 36–53
Chemical behaviour of alkyl imido cyclopentadienyl niobium and
tantalum(V) complexes in insertion processes. X-ray crystal
structures of [MCpCl(NAr){h2-C(Me)ꢀNAr}] (Ar=2,6-Me2C6H3;
M=Nb, Cpꢀh5-C5H4SiMe3; M=Ta, Cp=h5-C5Me5) and
[Ta(h5-C5Me5)Me(NAr){h2-C(CH2CMe2Ph)ꢀO}]
(Ar=2,6-Me2C6H3)
Aurora Castro, Mikhail V. Galakhov, Manuel Go´mez *, Pilar Go´mez-Sal,
Avelino Mart´ın, Fernando Sa´nchez
Departamento de Qu´ımica Inorga´nica, Uni6ersidad de Alcala´ de Henares, Campus Uni6ersitario, E-28871 Alcala´ de Henares, Spain
Received 15 July 1999; accepted 20 September 1999
Abstract
Pure imido h2-iminoacyl derivatives [MCpX(NAr){h2-C(R)ꢀNAr}] (Ar=2,6-Me2C6H3; M=Nb, Cp=h5-C5H4SiMe3=Cp%,
X=Cl, R=Me, 1; X=Me, R=NMe2, 2; Me, 3; X=R=CH2SiMe3, 4; CH2CMe3, 5; CH2Ph, 6; M=Ta, Cp=h5-C5Me5=
Cp*, X=Cl, R=Me, 7; CH2SiMe3, 8; CH2CMe2Ph, 9; CH2CMe3, 10; CH2C6H5, 11; 2-(CH2NMe2)C6H4, 12; NMe2, 13;
X=R=CH2SiMe3, 14; CH2CMe2Ph, 15; CH2CMe3, 16; CH2C6H5, 17; C6H5, 18) can be prepared by reaction of chloro alkyl or
dialkyl imido complexes MCpXR(NAr) with 1 equivalent of 2,6-Me2C6H3NC. Reaction of alkyl methyl imido complexes
TaCp*RMe(NAr) with 1 equivalent of isocyanide 2,6-Me2C6H3NC takes place with migration of alkyl or methyl group, leading
to the formation of a mixture of methyl h2-alkyliminoacyl [TaCp*Me(NAr){h2-C(R)ꢀNAr}] (Ar=2,6-Me2C6H3; R=CH2SiMe3,
19; CH2Ph, 21; CH2CMe2Ph, 23; CH2CMe3, 25; C6H5, 27; 2-(CH2NMe2)C6H4, 29; NMe2, 30) and alkyl h2-methyliminoacyl
[TaCp*R(NAr){h2-C(Me)ꢀNAr}] (Ar=2,6-Me2C6H3; R=CH2SiMe3, 20; CH2Ph, 22; CH2CMe2Ph, 24; CH2CMe3, 26; C6H5, 28)
complexes. Alkyl imido derivatives also react with CO to give alkyl h2-acyl [TaCp*X(NAr){h2-C(R)ꢀO}] (Ar=2,6-Me2C6H3;
X=R=CH2SiMe3, 31; CH2CMe2Ph, 32; CH2CMe3, 33; CH2Ph, 34), chloro h2-acyl (X=Cl, R=CH2CMe2Ph, 35; NMe2, 36)
and methyl h2-acyl (X=Me, R=CH2CMe2Ph, 37; CH2CMe3, 38) complexes. Dinuclear ene diolate complexes
[{TaCp*X(NAr)}2{m-h2-OC(R)ꢀC(R)O}] (Ar=2,6-Me2C6H3; X=Cl, R=CH2CMe3, 39; X=Me, R=2-(CH2NMe2)C6H4, 40)
are formed by reaction of the chloro and methyl alkyl imido derivatives with carbon monoxide, whereas using [TaCp*XR(NAr)]
(Ar=2,6-Me2C6H3; X=Cl, R=CH2CMe3; X=R=Ph) a different sequence of reactions takes place leading finally to oxo
h2-iminoacyl complexes [TaCp*X(O){h2-C(R)ꢀNAr}] (X=Cl, R=CH2CMe3, 41; X=R=Ph, 42). All compounds were
characterised by NMR (1H, 13C) spectroscopy and IR measurements. The molecular structures of 1, 7 and 37 were studied by
X-ray diffraction methods and are discussed. © 2000 Published by Elsevier Science S.A. All rights reserved.
Keywords: Niobium; Tantalum; Imido h2-iminoacyl, h2-acyl cyclopentadienyl complexes
1. Introduction
monoxide and isocyanides, is an important
organometallic reaction that has deservedly received
relevant synthetic, mechanistic and theoretical studies
[2]. The resulting metal-h2-acyl and metal-h2-iminoacyl
derivatives are key and versatile reactive intermediates
in many transition-metal-promoted stoichiometric and
catalytic organometallic transformations [3].
Transfer of alkyl groups from transition metals to
coordinated unsaturated molecules [1], such as carbon
* Corresponding author.
E-mail address: mgomez@inorg.alcala.es (M. Go´mez)
0022-328X/00/$ - see front matter © 2000 Published by Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00566-5

A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
37
In the last few years, we have realized extensive
research efforts on transition-metal complexes with
multiply bonded ligands, basically high-valent niobium
and tantalum complexes containing cyclopentadienyl
ligands and strong p-donor organoimido substituents
[4]. Further, we have recently reported [5] the reactions
of chloro methyl tantalum(V) complexes with carbon
monoxide and isocyanides. Following our recent work,
we report herein a systematic study of the insertion and
intramolecular rearrangement processes observed when
2,6-Me2C6H3NC and CO react with alkyl chloro, di-
alkyl and mixed alkyl derivatives of imido cyclopenta-
dienyl niobium and tantalum(V). All compounds were
fully characterized and further, some of them were
studied by X-ray diffraction methods.
CH2CMe3, 5; CH2Ph, 6; M=Ta, Cp=Cp*, X=Cl,
R=Me, 7; CH2SiMe3, 8; CH2CMe2Ph, 9; CH2CMe3,
10; CH2C6H5, 11; 2-(CH2NMe2)C6H4, 12; NMe2, 13;
X=R=CH2SiMe3, 14; CH2CMe2Ph, 15; CH2CMe3,
16; CH2C6H5, 17; C6H5, 18) (Scheme 1). The complex 7
was described by us before [5] and in this paper we only
discuss its study by X-ray diffraction.
In the case of dialkyl derivatives (X=R=alkyl) the
migration of the second alkyl group observed for
TaCp*Cl2Me2 [4a] does not take place and the presence
of an excess of isocyanide does not produce a second
insertion reaction in the M-C(alkyl) or M-C(iminoacyl)
bonds [1f,3d,i,j].
The addition of one equivalent of 2,6-Me2C6H3NC to
benzene-d6 solutions of the alkyl methyl imido com-
plexes under rigorously anhydrous conditions (sealed
NMR tube with hydrophobic internal surface) gives a
mixture of methyl h2-alkyliminoacyl [TaCp*Me(NAr)-
{h2-C(R)ꢀNAr}] (Ar=2,6-Me2C6H3; R=CH2SiMe3,
19; CH2Ph, 21; CH2CMe2Ph, 23; CH2CMe3, 25; C6H5,
27; 2-(CH2NMe2)C6H4, 29; NMe2, 30) and alkyl h2-
2. Results and discussion
2.1. Reactions with isocyanides
methyliminoacyl
[TaCp*R(NAr){h2-C(Me)ꢀNAr}]
When 2,6-Me2C6H3NC is added to n-hexane solu-
tions of the chloro alkyl or dialkyl imido complexes
[MCpXR(NAr)] (Ar=2,6-Me2C6H3; M=Nb, Cp=
Cp%; M=Ta, Cp=Cp*) an insertion reaction takes
place to give the stable 18-electron imido h2-iminoacyl
derivatives [MCpX(NAr){h2-C(R)ꢀNAr}] (Ar=2,6-
Me2C6H3; M=Nb, Cp=Cp%, X=Cl, R=Me, 1; X=
Me, R=NMe2, 2; Me, 3; X=R=CH2SiMe3, 4;
(Ar=2,6-Me2C6H3; R=CH2SiMe3, 20; CH2Ph, 22;
CH2CMe2Ph, 24; CH2CMe3, 26; C6H5, 28) complexes
1
in ratios determined from H-NMR spectra and shown
in Scheme 2.
When the same reaction is repeated at room temper-
ature (r.t.) by using n-hexane as solvent in
a
dry box, alkyl h2-methyliminoacyl (R=CH2SiMe3, 20;
Scheme 1.

38
A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
Scheme 2.
CH2Ph, 22) and methyl h2-alkyliminoacyl (R=CH2-
CMe2Ph, 23; CH2CMe3, 25; C6H5, 27) complexes, ma-
jor components in the already mentioned mixture, are
isolated as insoluble microcrystalline solids. Further,
when the resulting suspension of the above experiment
tadienyl (wC–C:1026 cm−1
) [11], trimethylsilylcy-
clopentadienyl (wC–H:838 cm−1) [12] rings and for the
trimethylsilyl substituent (las CH3:1249 cm−1) [12d,
13]. Absorptions due to the C(R)ꢀN, MꢀN, M–C
and M–Cl stretching vibrations are observed at
:1633(Nb), 1614(Ta) [14], 1305(Nb), 1322(Ta) [15],
631(Nb), 697(Ta) [16] and 356(Nb), 355(Ta) [12d, 17]
cm–1, respectively.
1
is evaporated to dryness, a H-NMR spectrum in ben-
zene-d6 of the crude residue gave the same result. Yields
reflect the relative case of migration [6] of a wide
variety of alkyl groups, such as 2 - (CH2NMe2)C6H4:
NMe2 \ CH2CMe2Ph : CH2C-Me3 \ C6H5 \ Me\
CH2SiMe3\CH2Ph as compared with methyl group.
Our particular contribution also establishes the regio-
selective migration of the 2-[(dimethylamino)methyl)]-
phenyl and dimethylamido groups. The preferential
migration of the NMe2 moiety, in the case of the
starting amido methyl niobium and tantalum deriva-
tives to give methyl h2-iminocarbamoyl complexes 2
and 30, is quite unusual because in similar amido alkyl
or methyl titanium [7], zirconium [8], tungsten [9] and
uranium [10] complexes the insertion occurs preferen-
tially at the metal–carbon (alkyl) bond.
1
The H- and 13C{1H}-NMR data (Table 2) of the
h2-iminoacyl complexes 1–30 is in agreement with the
expected pseudo-square-pyramidal geometry found for
similar chiral niobium and tantalum derivatives [5]. The
1H-NMR spectra show AB spin systems for
diastereotopic a-CH2 protons of alkyl groups in the
complexes 4–6, 8–12, 14–17, 20, 22–26 and 29, the
expected two resonances for the inequivalent methyl
substituents of the b-CMe2 groups in the 1H- and
13C{1H}-NMR spectra of 9, 15, 23 and 24 and four
proton and five carbon resonances for the trimethylsi-
lylcyclopentadienyl ring in the complexes 16 due to the
chiral character of the metal atoms. The observation of
two inequivalent methyl groups for the 2,6-Me2C6H3
moiety of the h2-iminoacyl ligand in the complexes
1–6, 8–13, 15–18, 20, 22, 23, 25, 27 and 30 is consis-
tent with the restricted rotation of the aryl group
around the N–Ci(aryl) bond, whereas the detection of
broad signals for ortho-methyl(phenyl) groups of the
imido ligand in the complexes 8–11, 1–17, 20, 22, 23,
25, 27 and 30 is due to a slow (on the NMR time scale)
rotation around the Nimido-Ci(aryl) bond.
Exactly the same h2-iminoacyl complexes 19–30 are
obtained by reaction of 2 equivalents of the isocyanide
with the starting mixed alkyl imido derivatives in ben-
zene-d6 solutions at r.t. The bis-(h2-iminoacyl) deriva-
1
tives cannot be detected by H-NMR spectroscopy.
All of the complexes 1–30 are soluble in aromatic,
chlorinated and ethereal solvents; further the complexes
2–5, 19, 21, 23, 24, 26 and 28 are soluble in saturated
hydrocarbons whereas the remaining complexes are
only slight soluble.
The h2-iminoacyl carbon signals appear at l:230
and 243 for niobium and tantalum derivatives, respec-
The IR spectra (Table 1) of all complexes show the
characteristic absorptions for the pentamethylcyclopen-

Table 1
IR a data of the new complexes
wC(R)ꢀN
wC(R)ꢀO
wMꢀN
wC–C(Cp*) wM–C
wM–Cl
Others
1
2
3
4
5
6
8
9
1655(m)
1636(s)
1307(m)
1313(s)
1312(s)
1300(vs)
1307(m)
1296(m)
1318(m)
1329(vs)
1247(m)[wls(Me3Si)], 1170(w), 1092(m), 1043(w), 902(w), 839(m), [wC–H(Cp%)], 630(w)
1462(vs), 1245(s)[wls(Me3Si)],1168(m), 1080(m), 1044(m), 905(m), 834(vs) [wC–H(Cp%)], 670(w), 474(w)
1243(m)[wls(Me3Si)], 1188(m), 1094(m), 1043(m), 906(m), 838(vs)[wC–H(Cp%)], 460(w)
1410(s), 1247(vs)[wls(Me3Si)],1180(s), 1096(m), 1043(m), 905(m),840(s)[wC–H(Cp%)], 674(w)
1410(s), 1247(m)[wls(Me3Si)], 1180(m), 1094(m), 1044(m), 906(m), 840(s)[wC–H(Cp%)], 698(w)
1461(vs),1247(m)[wls(Me3Si)], 1177(m), 1094(m), 1031(m), 904(m),836(s)[wC–H(Cp%)], 698(m)
1254(s)[wls(Me3Si)], 1188(m), 1098(m), 843(m), 673(m), 221(w)
629(w)
1639(m)
1613(m)
1635(m)
1621(m)
1585(m)
1655(vs)
633(w)
631(w)
632(w)
632(w)
1023(m)
1027(m)
351(w)
360(w)
1589(s), 1414(s), 1176(s), 1095(s), 983(m), 934(m), 919(m), 815(m), 757(vs), 741(m), 722(m), 699(m), 575(w), 548(w),
508(w), 300(m), 275(w), 217(w)
10 1603(m)
11 1619(s)
12 1603(vs)
13 1611(vs)
14 1574(s)
1310(vs)
1322(vs)
1312(vs)
1330(vs)
1330(vs)
1024(m)
1027(m)
1025(m)
1027(m)
1025(m)
351(w)
357(m)
358(w)
1585(m), 1094(m), 974(m), 836(w), 764(m), 392(w), 300(w), 221(w)
1589(s), 1588(m), 1180(m), 1093(s), 979(m), 918(m), 833(m),756(s), 702(m), 509(w), 469(w), 392(w), 298(m), 268(w)
1580(m), 1212(m), 1151(w) 923(m), 859(w), 803(w), 764(m), 722(m), 394(w), 244(w), 217(w)
1587(m), 1261(m), 1183(w), 1095(s), 803(m), 783(m), 758(w), 722(w)
1252(s)[wls(Me3Si)], 1148(w), 1096(s), 967(m), 947(m), 846(vs), 755(vs), 732(vs), 673(m), 462(w), 346(m), 266(w),
235(w), 221(w)
1591(m), 1415(m), 1179(m), 1095(m), 976(m), 758(m), 698(m), 344(m), 240(w)
1411(s), 1217(m), 1157(m), 1094(m), 969(m), 933(w), 808(w), 759(s), 727(s), 699(s), 619(w), 470(w), 390(w), 349(m),
292(w)
/
539(w)
570(w)
15 1644(m)
16 1580(s)
1321(s)
1315(vs)
1028(m)
1025(m)
17 1621(m)
18 1580(s)
1321(vs)
1315(vs)
1024(m)
1025(m)
573(w)
1590(m), 1201(m), 1171(m), 1094(m), 1056(m), 976(m), 826(m), 761(s), 739(vs), 697(s), 505(w), 469(w), 443(w),
391(w), 347(m), 256(w)
1411(s), 1217(m), 1157(m), 1094(m), 969(m), 933(w), 808(w), 759(s), 727(s), 699(s), 619(w), 470(w), 390(w), 349(m),
292(w)
20 1613(s)
22 1614(s)
23 1589(s)
25 1587(s)
27 1587(s)
29 1603(s)
30 1604(s)
31
32
33
35
37
38
39
1330(vs)
1331(vs)
1320(s)
1025(m)
1026(m)
1025(m)
1025(m)
1027(m)
1031(m)
1029(m)
1037(m)
1028(s)
1024(m)
1033(s)
1032(m)
1023(m)
1024(m)
1586(s), 1260(m)[wls(Me3Si)], 1187(w), 1093(m), 978(m), 825(m), 764(vs), 689(m), 480(w), 347(m), 265(w), 226(w)
1590(s), 1196(m), 1094(m), 979(m), 834(w), 761(s), 698(m), 352(m)
1183(m), 1095(m), 975(m), 757(s), 696(m), 477(w), 348(w)
9
1319(s)
1183(m), 1095(m), 974(w), 801(w), 761(m), 472(w), 392(w), 346(w), 274(w), 243(w)
1228(m), 1160(m), 1094(m), 977(w), 810(w), 759(m), 693(m), 485(w), 347(m), 286(w)
1580(s), 1210(m), 1152(m), 1094(m),976(m), 918(m), 858(w), 803(m), 762(vs), 721(m), 480(w), 351(m), 241(w)
1586(s), 1183(m), 1162(m), 1095(m), 1083(m), 983(w), 908(w), 784(m), 756(m), 722(w), 488(w)
1587(m), 1249(s)[wls(Me3Si)],1186(m), 1094(m), 948(s), 853(vs), 757(s), 671(m), 469(m), 354(m), 269(w)
1595(m), 1094(m), 976(w), 804(w), 760(vs), 700(vs), 348(m), 249(w)
1587(m), 1095(m), 983(w), 759(vs), 723(s), 606(m), 414(m), 347(s), 258(w)
1586(w), 1279(m), 1094(m), 983(w), 768(vs), 722(w), 700(s), 366(m), 313(m), 233(m)
1586(w), 1157(w), 1093(m), 980(w), 766(s), 700(m), 549(w), 484(m), 358(m)
1586(w), 1156(w), 1093(s), 1052(m), 979(m), 757(s), 722(m), 627(w), 352(w), 222(w)
1588(w)[wCꢀC], 1537(m), 1162(w)[wCꢀO], 1094(m), 1053(m), 981(w), 909(m), 822(w)[wTa–O], 762(vs), 723(s), 317(m),
215(w)
1325(vs)
1318(vs)
1332(vs)
1327(vs)
1313(vs)
1328(vs)
1330(vs)
1333(vs)
1332(vs)
1330(vs)
)
593(w)
580(m)
550(m)
3
1498(m)
1546(m)
1545(m)
1547(m)
1545(m)
1536(m)
366(m)
40
1334(vs)
1024(m)
1026(m)
1587(w)[wCꢀC], 1157(w)[wCꢀO], 1094(s), 981(m), 802(w)[wTa–O], 761(vs), 648(w), 605(m), 510(s), 474(m), 346(s)
1236(m), 1158(m), 1090(m), 940(w), 901(vs)[wTaꢀO], 809(w), 774(s), 726(s), 700(s), 352(m), 288(w), 250(w), 230(w)
42 1601(s)
a Nujol mull, w in cm−1
.

Table 2
1H- and 13C{1H}-NMR data of the new complexes a
1H
13C{1H}
1
2
a, 6.90(m, 4H), 6.71[m, 2H, H3C6Me2N, H3C6Me2NꢀC(Me)], 6.26(m, 1H), 6.23
(m, 1H), 6.09(m, 1H), 5.62(m, 1H, H4C5SiMe3), 2.49(s, 6H, Me2C6H3N), 2.04[s,
3H, (Me)CꢀNC6H3Me2], 1.92(s, 3H), 1.73[s, 3H, Me2C6H3NꢀC(Me)], 0.30(s, 9H,
Me3SiC5H4)
a, 225.89[C (Me)ꢀNC6H3Me2], 155.38, 139.84[Ci, C6H3Me2N, C6H3Me2NꢀC(Me)],132.13,
126.67, 122.8[several phenyl, C6H3Me2N,C6H3Me2NꢀC(Me)], 117.6(Ci,C5-
H4SiMe3),120.9, 112.7, 110.9,108.9 (C5H4SiMe3), 21.85[(Me)CꢀNC6H3Me2], 19.73
(Me2C6H3N), 18.26, 18.15[Me2C6H3NꢀC(Me)], −0.09(Me3SiC5H4)
a, not observed[C (NMe2)ꢀNC6H3Me2], 142.82, 140[Ci,C6H3Me2N,C6H3Me2NꢀC(NMe2)],
131.8, 127.5, 124.9, 120.6[several phenyl, C6H3Me2N,C6H3Me2NꢀC(NMe2)], 114.2(Ci,
C5H4SiMe3), 117.74, 110.3, 108.8, 106.6(C5H4SiMe3), 44.54, 36.13[(Me2N)CꢀNC6H3Me2],
20.27(Me2C6H3N), 18.75, 18.36[Me2C6H3NꢀC(NMe2)], 13.00(br, Me–Nb), −0.20(Me3SiC5H4)
a, 7.00(d, 2H, 3JH–H=7.5 Hz), 6.92(m, 1H), 6.87(t, 1H, 3JH–H=7.5 Hz), 6.82[m,
2H, H3C6Me2N,H3C6Me2NꢀC(NMe2)], 6.72(m, 1H), 6.12(m, 1H), 6.02(m, 1H),
5.52(m, 1H, H4C5SiMe3), 2.89[s, 3H, 1JC–H=136.6 Hz, (Me2N)CꢀNC6H3Me2],
2.50(s, 6H, 1JC–H=124.9 Hz, Me2C6H3N), 2.18 [s, 3H, 1JC–H=136.6 Hz,
(Me2N)CꢀNC6H3Me2], 1.86(s, 3H), 1.82[s, 3H, Me2C6H3NꢀC(NMe2)], 0.79(s, 3H,
Me–Nb), 0.21(s, 9H, Me3SiC5H4)
3
4
a, 6.93(d, 2H, 3JH–H=7.5 Hz), 6.87(m, 2H), 6.78(m, 1H), 6.68[t, 1H, H3C6Me2N, a, 229.1[C(Me)ꢀNC6H3Me2], 155.61, 141.5[Ci, C6H3Me2N,C6H3Me2NꢀC(Me)], 131.3, 129.03,
H3C6Me2NꢀC(Me)], 6.19(m, 1H), 5.99 (m, 1H), 5.73(m, 1H), 5.67(m, 1H, 126.5, 121.6[several phenyl, C6H3Me2N, C6H3Me2NꢀC(Me)], 113.1(Ci,C5H4SiMe3), 115.6,
H4C5SiMe3), 2.45(s, 6H, Me2C6H3N), 2.15[s, 3H, (Me)CꢀNC6H3Me2], 1.75(s, 3H), 112.8, 109.6, 109.1(C5H4SiMe3), 22.66[(Me)CꢀNC6H3Me2], 20.23(Me2C6H3N), 18.26,
1.59[s, 3H, Me2C6H3NꢀC(Me)], 0.89(s, 3H, Me–Nb), 0.20(s, 9H, Me3SiC5H4) 18.17[Me2C6H3NꢀC(Me)], 11.7(br, Me–Nb), 0.25(Me3SiC5H4)
a, 6.95(d, 2H), 6.86(m, 1H), 6.82(m, 1H), 6.77(m, 1H), 6.70[t, 1H, 3JH–H=7.2 Hz, a, 231.8[C(CH2SiMe3)ꢀNC6H3Me2], 155.6, 143.7[Ci, C6H3Me2N,C6H3Me2NꢀC(CH2SiMe3)],
/
H3C6Me2N, H3C6Me2NꢀC(CH2SiMe3)], 6.76(m, 1H), 6.27(m, 1H), 6.15(m, 1H),
132.3, 131.75, 129.4, 125.64[several phenyl, C6H3Me2N, C6H3Me2NꢀC(CH2SiMe3)], 121.4,
117.5, 109.3, 109.1(C5H4SiMe3), 109.44(Ci, C5H4SiMe3), 65.9(Nb–C H2SiMe3),
31.31[(CH2SiMe3)CꢀNC6H3Me2], 20.6(Me2C6H3N), 18.75, 18.6[Me2C6H3NꢀC(CH2SiMe3)],
3.64(Me3SiC5H4), 0.02(Me3SiCH2–Nb), −0.02[(Me3SiCH2)CꢀNC6H3Me2]
5.50 (m, 1H, H4C5SiMe3), 2.80, 2.07[AB, 2H, 2JH–H=16.2 Hz,
(H2CSiMe3)CꢀNC6H3Me2], 2.55(s, 6H, Me2C6H3N), 2.12(s, 3H), 1.78[s, 3H,
Me2C6H3NꢀC(CH2SiMe3)], 0.93AV(AB, 2H, 2JH–H=12.3 Hz, Nb–CH2SiMe3),
0.22(s, 9H, Me3SiC5H4), 0.06(s, 9H, Me3SiCH2–Nb), −0.18[s, 9H,
(Me3SiCH2)CꢀNC6H3Me2]
5
a, 7.07(m, 1H), 6.89(m, 4H), 6.69[t, 1H, 3JH–H=7.2 Hz, H3C6Me2N,
H3C6Me2NꢀC(CH2CMe3)], 7.00(m, 1H), 6.31(m, 1H), 6.14(m, 1H), 5.50(m, 1H,
H4C5SiMe3), 2.62, 2.02[AB, 2JH–H=12.6 Hz (Me3CCH2)CꢀNC6H3Me2], 2.58(s,
6H, Me2C6H3N), 2.48, 0.87(AB, 2JH–H=15 Hz, Nb–CH2CMe3), 2.03(s, 3H),
1.65[s, 3H, Me2C6H3NꢀC(CH2CMe3)], 1.12(s, 9H, Me3CCH2–Nb), 0.99[s, 9H,
(Me3CCH2)CꢀNC6H3Me2], 0.20(s, 9H, Me3SiC5H4)
a, 232.8[C(CH2CMe3)ꢀNC6H3Me2], 155.8, 144[Ci, C6H3Me2N,C6H3Me2NꢀC(CH2CMe3)],
131.5, 129.7, 128.8, 126.3, 121.7[several phenyl, C6H3Me2N,C6H3Me2NꢀC(CH2CMe3)],
113.4(Ci, C5H4SiMe3), 116.9, 110.13, 109.7, 108.6(C5H4SiMe3), 62(Nb–CH2CMe3),
51.2[(CH2CMe3)CꢀNC6H3Me2], 46.9(Me3CCH2–Nb), 35.7[(Me3CCH2)CꢀNC6H3Me2],
35.5[(Me3CCH2)CꢀNC6H3Me2], 30.45(Me3CCH2–Nb), 21.3(Me2C6H3N), 18.6, 18.5[Me2-
C6H3NꢀC(CH2CMe3)], 0.58(Me3SiC5H4)
9
6
8
9
a, 7.05(m, 3H), 6.94(m, 8H), 6.75[m, 5H, H3C6Me2N, H3C6Me2NꢀC(CH2C6H5),
Nb–CH2C6H5], 6.39(m, 1H), 5.93(m, 1H), 5.32(m, 1H), 5.20(m, 1H,H4C5SiMe3),
3.72AV[AB, 2H, 2JH–H=14.8 Hz, (CH2Ph)CꢀNC6H3Me2], 3.27AV(AB, 2H,
2JH-H=10.2 Hz, Nb–CH2Ph), 2.48(s, 6H, Me2C6H3N), 1.70(s, 3H), 1.45[s, 3H,
Me2C6H3NꢀC(CH2Ph)], 0.13(s, 9H, Me3SiC5H4).
a,230[C(CH2Ph)=NC6H3Me2], 155.42, 153.51, 141.8(Ci,
(
C6H3Me2N,C6H3Me2NꢀC(CH2C6H5), Nb–CH2C6H5], 132.2, 131, 130.1, 129, 126.4, 121.8,
121[several phenyl, C6H3Me2N, C6H3Me2NꢀC(CH2C6H5),Nb–CH2C6H5], 115(Ci,
C5H4SiMe3), 117.74, 113.1, 111.4, 108 (C5H4SiMe3), 43.42[(CH2Ph)CꢀNC6H3Me2], 40.1(br,
Nb–CH2Ph), 20.5(Me2C6H3N), 18.4, 18[Me2C6H3NꢀC(CH2Ph)], −0.25(Me3SiC5H4)
3
b, 7.00(m, 3H, H3C6Me2NꢀC(CH2SiMe3)], 6.86(d, 2H, 3JH–H=7.5 Hz), 6.55(t, 1H, b, 259.90[C(CH2SiMe3)=NC6H3Me2], 153.43–120.05[several phenyl, C6H3Me2N,
3JH–H=7.5 Hz, H3C6Me2N), 2.90, 2.84 [AB, 2H, 2JH–H=15 Hz,
(H2CSiMe3)CꢀNC6H3Me2], 2.28(br, 6H, Me2C6H3N), 2.05(s, 15H, C5Me5), 2.06(s, Me2C6H3N), 18.95, 18.68[Me2C6H3NꢀC(CH2SiMe3)], 11.30(C5Me5),
C6H3Me2NꢀC(CH2SiMe3)], 115.55(C5Me5), 29.56[(CH2CSiMe3)CꢀNC6H3Me2], 19.70(br,
3H), 1.90 [s, 3H, Me2C6H3NꢀC(CH2SiMe3)], −0.07[s, 9H,
(Me3SiCH2)CꢀNC6H3Me2]
0.52[(Me3SiCH2)CꢀNC6H3Me2]
b, 7.15(m, 2H), 6.96[m, 3H, (H5C6Me2CCH2)CꢀNC6H3Me2], 7.15[m,
3H,H3C6Me2NꢀC(CH2CMe2Ph)], 6.87 (d, 2H, 3JH–H=7.3 Hz), 6.57(t, 1H,
3JH–H=7.3 Hz, H3C6Me2N), 3.50[q, 2H, 2JH–H=14.65 Hz,
(H2CCMe2Ph)CꢀNC6H3Me2], 2.30(br, 6H, Me2C6H3N), 2.00(s, 15H, C5Me5),
1.86(s, 3H), 1.64[s, 3H, Me2C6H3NꢀC(CH2CMe2Ph)], 1.51(s, 3H), 1.21[s, 3H,
(Me2PhCCH2)CꢀNC6H3Me2]
b, 238.31[C(CH2CMe2Ph)=NC6H3Me2], 153.35–120.28[several phenyl, C6H3Me2N,
C6H3Me2NꢀC(CH2CMe2C6H5)], 115.84(C5Me5), 51.13[(CH2CMe2Ph)CꢀNC6H3Me2],
38.94[(CH2CMe2Ph)CꢀNC6H3Me2], 30.68, 29.36[(CH2CMe2Ph)CꢀNC6H3Me2],
20.01(Me2C6H3N), 18.60, 18.53[Me2C6H3NꢀC(CH2CMe2Ph)], 11.30(C5Me5)

Table 2 (Continued)
1H
13C{1H}
3
10
11
12
b, 7.02[m, 3H, H3C6Me2NꢀC(CH2CMe3)], 6.86(d, 2H, JH–H=7.5 Hz),
b, 238.73[C(CH2CMe3)=NC6H3Me2], 153.47–120.27[several phenyl, C6H3Me2N,
C6H3Me2NꢀC(CH2CMe3)], 115.93(C5Me5), 50.24[(CH2CMe3)CꢀNC6H3Me2],
33.14[(CH2CMe3)CꢀNC6H3Me2], 30.92[(CH2CMe3)CꢀNC6H3Me2], 20(br,Me2C6H3N), 18.78,
18.66[Me2C6H3NꢀC(CH2CMe3)], 11.4(C5Me5)
3
2
6.57(t, 1H, JH–H=7.5 Hz, H3C6Me2N), 2.95[q, 2H, JH–H=13.18 Hz,
(H2CCMe3)CꢀNC6H3Me2], 2.30(br, 6H, Me2C6H3N), 2.04(s, 15H, C5Me5),
2.06(s, 3H), 1.77[s, 3H, Me2C6H3NꢀC(CH2CMe3)], 0.98[s, 9H,
(Me3CCH2)CꢀNC6H3Me2]
b, 7.15(m, 2H), 6.93[m, 3H, (H5C6CH2)CꢀNC6H3Me2], 7.10[m, 3H,
H3C6Me2NꢀC(CH2Ph)], 6.87(d, 2H, JH–H=7.35 Hz), 6.56(t, 1H, JH–H
b, 237.77[C(CH2Ph)=NC6H3Me2], 140.86–120.4[several phenyl, C6H3Me2N,
C6H3Me2NꢀC(CH2C6H5)], 115.86(C5Me5), 43.00[(CH2Ph)CꢀNC6H3Me2], 19.3(br, Me2C6H3N),
18.6, 18.34[Me2C6H3NꢀC(CH2Ph)], 11.31(C5Me5)
3
3
=
2
7.35 Hz, H3C6Me2N), 4.41, 4.27[AB, 2H, JH–H=15.38 Hz, (PhCH2)CꢀNC6-
H3Me2], 2.23(br, 6H,Me2C6H3N), 2.02(s, 15H,C5Me5), 1.86(s, 3H), 1.76[s,
3H,Me2C6H3NꢀC(CH2Ph)]
b, 8.05(m, 1H), 7.67(m, 1H), 7.43(m, 2H), 7.07(d, 1H), 6.98(t, 1H), 6.76[d, 1H,
b, 237.15[{H4C6(2-CH2NMe2)}C=NC6H3Me2], 153.72–120.73[several phenyl, C6H3Me2N,
{H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 116.14(C5 Me5), 60.17[{H4C6(2-
CH2NMe2)}CꢀNC6H3Me2], 45.07[{H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 20.27(Me2C6H3N),
20.06, 18.53[{H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 11.32(C5Me5)
3
{H4C6(2-CH2NMe2)} CꢀNC6H3Me2], 6.88(d, 2H, JH–H=7.7 Hz), 6.58(t, 1H,
3JH–H=7.7 Hz, H3C6Me2N), 2.75, 2.56 [AB, 2H, JH–H=13.50 Hz, {H4C6(2-
2
CH2NMe2)}CꢀNC6H3Me2], 2.45(s, 6H, Me2C6H3N), 2.05(s, 15H, C5Me5),
2.29(s, 3H), 1.38[s, 3H, {H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 1.94[s, 6H,
{H4C6(2-CH2NMe2)}CꢀNC6H3Me2]
/
3
13
14
b, 6.92[m, 3H, H3C6Me2NꢀC(NMe2)], 6.86(d, 2H, JH–H=7.2 Hz), 6.52(t, 1H,
b, 200.23[C(NMe2)=NC6H3Me2], 153.97–119.41[several phenyl, C6H3Me2N, C(NMe2)=
NC6H3Me2], 116(C5Me5), 45.37, 37.76[H3C6Me2NꢀC(NMe2)], 19.55(br,Me2C6H3N), 19.27,
18.75[Me2C6H3NꢀC(NMe2)], 11.63(C5Me5)
3JH–H=7.2 Hz, H3C6Me2N), 3.46(s, 3H), 2.70[s, 3H, H3C6Me2NꢀC(NMe2)],
2.27(br, 6H,Me2C6H3N), 2.09(s, 15H, C5Me5), 1.98(s, 3H), 1.88[s, 3H,
Me2H3C6NꢀC(NMe2)]
3
b, 7.00(br, 3H, H3C6Me2NꢀC(CH2SiMe3)], 6.87(d, 2H, JH–H=7.5 Hz), 6.52(t, 1H, b, 244.78[C(CH2SiMe3)=NC6H3Me2], 154.5–118.69[several phenyl, C6H3Me2N,
3JH–H=7.5 Hz, H3C6Me2N), 3.45, 2.35[AB, 2H, JH–H=12.82 Hz,
C(CH2SiMe3)=NC6H3Me2], 112.7(C5Me5), 28.38, 22.41[C(CH2SiMe3)=NC6H3Me2, Ta–
CH2SiMe3], 18.86(br, Me2H3C6N), 19.30[H3C6Me2NꢀC(CH2SiMe3)], 11.23(C5Me5), 3.41,
0.77[C(CH2SiMe3)=NC6H3Me2, Ta–CH2SiMe3]
2
H3C6Me2NꢀC(CH2SiMe3)], 2.21(s, 6H, Me2H3C6N), 1.94(s, 15H, C5Me5), 1.94[s,
6H, H3C6Me2NꢀC(CH2SiMe3)], −0.12[s, 9H, H3C6Me2NꢀC(CH2SiMe3)], −0.45(s,
2
9H, Ta–CH2SiMe3), −0.16, −0.67(AB, 2H, JH–H=12.45 Hz, Ta–CH2SiMe3)
15
b, 7.15(m, 4H), 7.05(m, 3H), 7.00(m, 1H), 6.83[m, 2H,
b, 244.68[[C(CH2CMe2Ph)=NC6H3Me2], 159.15–119.26[several phenyl, C6H3Me2N,
(H5C6Me2CCH2)CꢀNC6H3Me2, Ta–CH2CMe2C6H5], 113.24(C5Me5), 58.42, 52.00(Ta–
CH2CMe2Ph], 40.52, 38.81[(PhMe2CCH2)CꢀNC6H3Me2], 33.75, 32.51, 31.30, 29.90[Ta–
CH2CMe2Ph, (PhMe2CCH2)CꢀNC6H3Me2], 20.71(Me2H3C6N), 18.97,
18.54[(PhMe2CCH2)CꢀNC6H3Me2], 11.14(C5Me5)
(H5C6Me2CCH2)CꢀNC6H3Me2, Ta–CH2CMe2C6H5], 7.06[m, 3H,
3
(H5C6Me2CCH2)CꢀNC6H3Me2], 6.90(d, 2H, JH–H=7.5 Hz), 6.56(t, 1H,
2
3JH–H=7.5 Hz, H3C6Me2N), 4.16, 3.51 [AB, 2H, JH–H=16.85 Hz,
5
(PhMe2CCH2)CꢀNC6H3Me2], 2.26(br, 6H, Me2C6H3N), 1.85(s, 15H, C5Me5),
1.67(s, 3H), 1.53[s, 3H, (PhMe2CCH2)CꢀNC6H3Me2], 1.50, 0.95(AB, 2H, JH–H
2
=
)
11.35 Hz, Ta–CH2CMe2Ph), 1.22[br, 6H, Ta–CH2CMe2Ph], 1.21(s, 3H), 0.78[s, 3H,
(PhMe2CCH2)CꢀNC6H3Me2]
3
3
16
17
18
b, 7.00[m, 3H, (Me3CCH2)CꢀNC6H3Me2], 6.88(d, 2H, JH–H=7.2 Hz),
b, 246.47[C(CH2CMe3)=NC6H3Me2], 154.55–119[several phenyl, C6H3Me2N,
(Me3CCH2)CꢀNC6H3Me2], 113.06(C5Me5), 57.75, 50.64[Ta–CH2CMe3,
(Me3CCH2)CꢀNC6H3Me2], 33.83, 33.11[Ta–CH2CMe3, (Me3CCH2)CꢀNC6H3Me2], 35.79, 31.43
[Ta–CH2CMe3, (Me3CCH2)CꢀNC6H3Me2], 20.55, 19.27[(Me3CCH2)CꢀNC6H3Me2], 18.90(br,
Me2C6H3N), 11.18(C5Me5)
3
2
6.54(t, 1H, JH–H=7.2 Hz, H3C6Me2N), 3.76, 2.74[AB, 2H, JH–H=15.30 Hz,
(Me3CCH2)CꢀNC6H3Me2], 2.29(s, 6H, Me2C6H3N), 1.92(s, 15H, C5Me5),
2
1.95(s, 3H), 1.85[s, 3H, (Me3CCH2)CꢀNC6H3Me2], 1.25, 0.50(AB, 2H, JH–H
14.10 Hz, Ta–CH2CMe3), 0.86(s, 9H, Ta–CH2CMe3), 0.67[s, 9H,
(Me3CCH2)CꢀNC6H3Me2]
=
b, 7.10[m, 3H, (PhCH2)CꢀNC6H3Me2], 6.91(m, 2H), 6.74(m, 4H), 6.44(m, 3H),
b, 240.55[C(CH2Ph)=NC6H3Me2], 154.29–119.34[several phenyl, C6H3Me2N,
(C6H5CH2)CꢀNC6H3Me2, Ta–CH2C6H5], 113.65(C5Me5), 46.95,
42.17[(C6H5CH2)CꢀNC6H3Me2, Ta–CH2C6H5], 19.94(br, Me2C6H3N), 18.46,
3
6.33[m, 1H, (H5C6CH2)CꢀNC6H3Me2, Ta–CH2C6H5], 6.96(d, 2H, JH–H=7.3 Hz),
3
2
6.61(t, 1H, JH–H=7.3 Hz, H3C6Me2N), 4.32, 4.03[AB, 2H, JH–H=14.65 Hz,
2
(PhCH2)CꢀNC6H3Me2], 2.81, 1.81(AB, 2H, JH–H=11.35 Hz, Ta–CH2Ph), 2.34(br, 18.30[(C6H5CH2)CꢀNC6H3Me2], 11.03(C5Me5)
6H, Me2C6H3N), 1.90(s, 15H, C5Me5), 1.72(s, 3H), 1.29[s, 3H, (PhCH2)Cꢀ
NC6H3Me2]
b, 7.66(m, 2H), 7.58(m, 2H), 7.44(m, 1H), 7.40(m, 2H), 6.92(m, 2H), 6.84(m, 3H),
b, 232.57[(Ph)C=NC6H3Me2], 181.52–119.30[several phenyl, C6H3Me2N, (C6H5)CꢀNC6H3Me2,
Ta–C6H5], 114.91(C5Me5), 20.64(Me2C6H3N), 18.83, 18.45[(Ph)CꢀNC6H3Me2], 12(C5Me5)
3
6.73[m, 1H, (H5C6)CꢀNC6H3Me2, Ta–C6H5], 6.85(d, 2H, JH–H=7.3 Hz),
3
6.54(t, 1H, JH–H=7.3 Hz, H3C6Me2N), 2.25(s, 6H, Me2C6H3N), 2.03(s, 15H,
C5Me5), 1.86(s, 3H), 1.60[s, 3H, (Ph)CꢀNC6H3Me2]

Table 2 (Continued)
1H
13C{1H}
19
20
bb, 1.98(s, 15H, C5Me5), 0.16(s, 3H, Ta–Me), 0.05[s, 9H,
(CH2SiMe3)CꢀNC6H3Me2]
bb, 241.67[(CH2SiMe3)C=NC6H3Me2], 112.75(C5Me5), 20.35[(CH2SiMe3)CꢀNC6H3Me2],
19.07(Ta–Me), 10.96(C5Me5), 1.01[(CH2SiMe3)CꢀNC6H3Me2]
b, 243[(Me)C=NC6H3Me2], 154.24–118.97[several phenyl, C6H3Me2N, (Me)CꢀNC6H3Me2],
112.87(C5Me5), 23.51(Ta–CH2SiMe3), 20.45[(Me)CꢀNC6H3Me2], 19.62, 18.92(br, Me2C6H3N),
18.63, 18.36[(Me)CꢀNC6H3Me2], 11(C5Me5), 3.28(Ta–CH2SiMe3)
b, 7.02[m, 3H, (Me)CꢀNC6H3Me2], 6.87(d, 2H, 3JH–H=7.32 Hz), 6.52(t, 1H,
3JH–H=7.32 Hz, H3C6Me2N), 2.58[s, 3H, (Me)CꢀNC6H3Me2], 2.24(br, 3H),
2.18(br, 3H, Me2C6H3N), 1.93(s, 15H, C5Me5), 1.88(s, 3H), 1.85[s, 3H,
(Me)CꢀNC6H3Me2], −0.43(s, 9H, Ta–CH2SiMe3), −0.08, −0.64(AB, 2H,
2JH–H=12.45 Hz, Ta–CH2SiMe3)
21
22
bb, 4.10[AB, 2H, 2JH–H=14.4 Hz, (C6H5CH2)CꢀNC6H3Me2], 1.90(s, 15H, C5Me5),
0.11(s, 3H, Ta–Me)
b, 6.94(m, 2H), 6.83(d, 2H), 6.59(t, 1H), 6.52(m, 1H), 6.45[t, 2H,
(Me)CꢀNC6H3Me2, Ta–CH2C6H5], 6.75(d, 2H, 3JH–H=7.2 Hz), 6.27(t, 1H,
3JH–H=7.2 Hz, H3C6Me2N), 2.51(br, 3H), 2.13(br, 3H, Me2C6H3N), 2.48, 1.82
(AB, 2H, 2JH–H=11.72 Hz, Ta–CH2Ph), 2.44[s, 3H, (Me)CꢀNC6H3Me2],
2(s, 15H, C5Me5), 1.80(s, 3H), 1.25[s, 3H, (Me)CꢀNC6H3Me2]
b, 7.12[m, 3H, (PhMe2CCH2)CꢀNC6H3Me2], 7.13(m, 1H), 7.03 (m, 2H), 6.90(m,
1H), 6.74[m, 1H, (H5C6Me2CCH2)CꢀNC6H3Me2], 6.87(d, 2H, 3JH–H=7.5 Hz),
6.40(t, 1H, 3JH–H=7.5 Hz, H3C6Me2N), 3.08, 3.04[AB, 2H, 2JH–H=13.5 Hz,
(CH2CMe2Ph)CꢀNC6H3Me2], 2.10(br, 6H, Me2C6H3N), 1.80(s, 15H, C5Me5),
1.79(s, 3H), 1.50 [s, 3H,(CH2CMe2Ph)CꢀNC6H3Me2], 1.63(s, 3H), 1.10[s, 3H,
(CH2CMe2Ph)CꢀNC6H3Me2], 0.00(s, Ta–Me)
b, 242.32[(Me)C=NC6H3Me2], 151.70–119.28 [several phenyl, C6H3Me2N, (Me)CꢀNC6H3Me2,
Ta–CH2C6H5], 113.16(C5Me5), 46.54(Ta–CH2Ph), 19.88[(Me)CꢀNC6H3Me2], 18.41, 17.97
[(Me)CꢀNC6H3Me2], 17.60(br, Me2C6H3N), 10.91(C5Me5)
/
23
b, 239.71[(CH2CMe2Ph)C=NC6H3Me2], 154.95–118.69[several phenyl, C6H3Me2N,
(CH2CMe2C6H5)CꢀNC6H3Me2], 113.80(C5Me5), 49.70[(CH2CMe2Ph)CꢀNC6H3Me2],
38.87[(CH2CMe2Ph)CꢀNC6H3Me2], 30.07, 29.42[(CH2CMe2Ph)CꢀNC6H3Me2], 21.82(Ta–Me),
20.02(Me2C6H3N), 18.44, 18.19[(CH2CMe2Ph)CꢀNC6H3Me2], 11.13(C5Me5)
24
25
bb, 2.80[s, 3H, (Me)CꢀNC6H3Me2], 2.14(s, 15H, C5Me5), 1.86, 1.44(AB, 2H,
2JH–H=13.5 Hz, Ta–CH2CMe2Ph)
bb, 244.08[(Me)C=NC6H3Me2], 113.44(C5Me5), 60.94(Ta–CH2CMe2Ph),
20.62[(Me)CꢀNC6H3Me2], 11.18(C5Me5)
b, 239.95[(Me3CCH2)C=NC6H3Me2], 155.05–118.60[several phenyl, C6H3Me2N,
(Me3CCH2)CꢀNC6H3Me2], 112.95(C5Me5), 49.44[(Me3CCH2)CꢀNC6H3Me2],
32.74[(Me3CCH2)CꢀNC6H3Me2], 30.83[(Me3CCH2)CꢀNC6H3Me2], 21.84(Ta–Me), 19.97(br,
Me2C6H3N), 18.50, 18.23[(Me3CCH2)CꢀNC6H3Me2], 11.19(C5Me5)
b, 7.03[m, 3H, (Me3CCH2)CꢀNC6H3Me2], 6.85(d, 2H, 3JH–H=7.32 Hz), 6.50(t,
1H, 3JH–H=7.32 Hz, H3C6Me2N), 2.77, 2.66[AB, 2H, 2JH–H=12.68 Hz,
(Me3CCH2)CꢀNC6H3Me2], 2.44(br, 6H,Me2C6H3N), 1.95(s, 15H, C5Me5),
2.01(s, 3H), 1.65 [s, 3H, (Me3CCH2)CꢀNC6H3Me2], 1.05[s, 9H,
(Me3CCH2)CꢀNC6H3Me2], 0.13(s, 3H, Ta–Me)
9
26
27
bb, 2.61[s, 3H, (Me)CꢀNC6H3Me2], 1.94(s, 15H, C5Me5)
bb, 240.45[(Me)C=NC6H3Me2], 115.54(C5Me5), 35.58[(Me)CꢀNC6H3Me2], 11.16(C5Me5)
b, 232.34[(C6H5)C=NC6H3Me2], 154.96–118.74[several phenyl, C6H3Me2N,
(C6H5)CꢀNC6H3Me2], 113.08(C5Me5), 19.87(Ta–Me), 18.68(Me2C6H3N), 18.22,
18.07[(C6H5)CꢀNC6H3Me2], 11.20(C5Me5)
(
b, 7.62(m, 3H), 7.41(m, 2H), 7.07(m, 1H), 7.02(t, 1H), 6.90[m, 2H,
(C6H5)CꢀNC6H3Me2], 6.85(d, 2H, 3JH–H=7.70 Hz), 6.50(t, 1H, 3JH–H=7.70 Hz,
H3C6Me2N), 2.26(br, 6H, Me2C6H3N), 1.98(s, 15H, C5Me5), 1.96(s, 3H), 1.57 [s,
3H, (C6H5)CꢀNC6H3Me2], 0.23(s, 3H, Ta–Me)
6
28
29
bb, 2.64[s, 3H, (Me)CꢀNC6H3Me2], 1.90(s, 15H, C5Me5)
bb, 240.48[(Me)C=NC6H3Me2], 114.11(C5Me5), 20.65[(Me)CꢀNC6H3Me2], 11.30(C5Me5)
b, 239.86[{H4C6(2-CH2NMe2)}C=NC6H3Me2], 155.19–119.06[several phenyl, C6H3Me2N,
{H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 113.10 (C5Me5), 60.24[{H4C6(2-
CH2NMe2)}CꢀNC6H3Me2], 45.14[{H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 20.13(Ta–Me),
20.58(Me2C6H3N), 19.39, 18.62[{H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 11.10(C5Me5)
b, 7.92(m, 1H), 7.64(m, 1H), 7.37[m, 2H, {H4C6(2-CH2NMe2)}CꢀNC6H3Me2],
7.04(d, 1H), 6.96(t, 1H), 6.77[d, 1H, 3JH–H=7.59 Hz, {H4C6(2-
CH2NMe2)}CꢀNC6H3Me2], 6.86(d, 2H, 3JH–H=7.40 Hz), 6.52(t, 1H,
3JH–H=7.40 Hz, H3C6Me2N), 2.80, 2.74[AB, 2H, 2JH–H=14.85 Hz, {H4C6(2-
CH2NMe2)}CꢀNC6H3Me2], 2.34(s, 6H, Me2C6H3N), 2.15(s, 3H), 1.35[s, 3H,
{H4C6(2-CH2NMe2)}CꢀNC6H3Me2], 1.97[s, 6H, {H4C6(2-CH2NMe2)}-
CꢀNC6H3Me2], 1.96(s, 15H, C5Me5), 0.35(s, 3H, Ta–Me)
30
b, 6.90[m, 3H, (Me2N)CꢀNC6H3Me2], 6.84(d, 2H, 3JH–H=7.20 Hz), 6.47(t,
b, 199.69[(Me2N)C=NC6H3Me2], 155.45–117.73[several phenyl, C6H3Me2N,
(Me2N)CꢀNC6H3Me2], 112.87(C5Me5), 45.54, 37.32[(Me2N)CꢀNC6H3Me2], 20.09(Ta–Me),
19.55(br, Me2C6H3N), 19.07, 18.60[(Me2N)CꢀNC6H3Me2], 11.34(C5Me5)
1H, 3JH–H=7.20 Hz, H3C6Me2N), 3.47(s, 3H), 2.67[s, 3H,
(Me2N)CꢀNC6H3Me2], 2.17(br, 6H, Me2C6H3N), 2.00(s, 15H, C5Me5), 1.92(s,
3H), 1.79[s, 3H, (Me2N)CꢀNC6H3Me2], −0.028(s, 3H, Ta–Me).

Table 2 (Continued)
1H
13C{1H}
3
3
31
a, 7.08(d, 2H, JH–H=7.8 Hz), 6.74(t, 1H, JH–H=7.8 Hz, H3C6Me2N),
a, 317.78[(Me3SiCH2)C=O], 154.7, 131.17, 127.44, 120.53(Ci, Co, Cm, Cp, C6H3Me2N),
113.5(C5Me5), 37.92[(Me3SiCH2)CꢀO], 29.11(Ta–CH2SiMe3), 19.82(Me2C6H3N), 10.9(C5Me5),
4.37[(Me3SiCH2)CꢀO], 0.096(Ta–CH2SiMe3)
2
3.68, 2.43 [AB, 2H, JH–H=11.1 Hz, (Me3SiCH2)CꢀO], 2.48(s, 6H,
Me2C6H3N), 1.69(s, 15H, C5Me5), 0.47, 0.19(AB, 2H, JH–H=11 Hz,
2
Ta–CH2SiMe3), 0.41[s, 9H, (Me3SiCH2)CꢀO], 0.05(s, 9H, Ta–CH2SiMe3)
32
a, 7.68(d, 2H), 7.26(m, 4H), 7.11(m, 2H), 7.03[m, 2H, (H5C6Me2CCH2)CꢀO,
a, 315.4[(PhMe2CCH2)C=O], 157.87–120.79[several phenyl, C6H3Me2N, (C6H5Me2CCH2)CꢀO,
Ta–CH2CMe2C6H5], 113.62(C5Me5), 61.7, 58.32[(PhMe2CCH2)CꢀO, Ta–CH2CMe2Ph], 42.73,
37.83[(PhMe2CCH2)CꢀO, Ta–CH2CMe2Ph], 34.9, 33.05, 28.93, 28.3[(PhMe2CCH2)CꢀO, Ta–
CH2CMe2Ph], 20.48(Me2C6H3N), 10.73(C5Me5)
3
3
Ta–CH2CMe2C6H5], 7.08(d, 2H, JH–H=7.5 Hz), 6.78(t, 1H, JH–H=7.5 Hz,
2
H3C6Me2N), 3.98, 3.4[AB, 2H, JH–H=20.5 Hz, (PhMe2CCH2)CꢀO], 2.34(s,
6H, Me2C6H3N), 1.60(s, 3H), 1.56[s, 3H, (PhMe2CCH2)CꢀO], 1.78, 1.6(AB, 2H,
2JH–H=13.5 Hz, Ta–CH2CMe2Ph), 1.57(s, 15H, C5Me5), 1.37(s, 3H), 1.32(s, 3H,
Ta–CH2CMe2Ph)
3
3
33
34
35
b, 6.88(d, 2H, JH–H=7.5 Hz), 6.56 (t, 1H, JH–H=7.5 Hz, H3C6Me2N), 3.8,
b, 317.47[(Me3CCH2)C=O], 154.18, 131.54, 126.75, 119.58(Ci, Co, Cm, Cp, C6H3Me2N),
113.5(C5Me5), 62.11, 57.28[(Me3CCH2)CꢀO, Ta–CH2CMe3], 36.02, 31.66[(Me3CCH2)CꢀO, Ta–
CH2CMe3], 35.28, 29.65[(Me3CCH2)CꢀO, Ta–CH2CMe3], 20.05(Me2C6H3N), 10.91 (C5Me5)
2
3.07[AB, 2H, JH–H=20 Hz, (Me3CCH2)CꢀO], 2.22(s, 6H, Me2C6H3N),
2
1.87(s, 15H, C5Me5), 1.24, 1.01(AB, 2H, JH–H=13.04 Hz, Ta–CH2CMe3),
1.10(s, 9H, Ta–CH2CMe3), 0.98[s, 9H, (Me3CCH2)CꢀO]
a, 7.53(d, 2H), 7.12(m, 5H), 7.00 (m, 2H), 6.80[m, 1H, (H5C6CH2)CꢀO, Ta–
a, 313.26[(PhCH2)C=O], 153.58–122.03[several phenyl, C6H3Me2N, (H5C6CH2)CꢀO, Ta–
CH2C6H5], 117.31(C5Me5), 58.57[(PhCH2)CꢀO], 49.97(Ta–CH2Ph), 19.4 (Me2C6H3N),
10.57(C5Me5)
/
3
3
CH2C6H5], 7.06(d, 2H, JH–H=7.2 Hz), 6.77(t, 1H, JH–H=7.2 Hz, H3C6Me2N),
2
4.30, 4.02[AB, 2H, JH–H=17.58 Hz, (PhCH2)CꢀO], 3.05, 2.37(AB, 2H,
2JH–H=11.35 Hz, Ta–CH2Ph), 2.33(s, 6H,Me2C6H3N), 1.64(s, 15H, C5Me5)
a, 7.2(m, 2H), 7.09(t, 2H), 7.01[m, 1H, (H5C6Me2CCH2)CꢀO], 7.00(d, 2H,
a, 315.17[(PhMe2CCH2)C=O], 153.25–122.2[several phenyl, C6H3Me2N, (H5C6Me2CCH2)CꢀO],
116.16(C5Me5), 58.48[(PhMe2CCH2)CꢀO], 38.31[(PhMe2CCH2)CꢀO], 29.37,
27.53[(PhMe2CCH2)CꢀO], 19.54(Me2C6H3N),10.91 (C5Me5)
3JH–H=7.2 Hz), 6.71(t, 1H, JH–H=7.2 Hz, H3C6Me2N), 3.62[q, 2H,
3
2JH–H=19.5 Hz, (PhMe2CCH2)CꢀO], 2.46(s, 6H, Me2C6H3N), 1.72(s, 15H,
C5Me5), 1.37(s, 3H), 1.23[s, 3H, (PhMe2CCH2)CꢀO]
3
3
36
37
b, 6.86(d, 2H, JH–H=7.4 Hz), 6.55 (t, 1H, JH–H=7.2 Hz, H3C6Me2N),
3.46(s, 3H), 3.26[s, 3H, (Me2N)CꢀO], 2.31(s, 6H, Me2C6H3N), 2.06(s, 15H,C5Me5)
a, 7.22(m, 2H), 7.11(m, 2H), 6.98[m, 1H, (H5C6Me2CCH2)CꢀO], 7.06(d,
b, 227.97[(Me2N)C=O], 153.14, 131.92, 126.6, 120.93(Ci, Co, Cm, Cp, C6H3Me2N), 116.76
(C5Me5), 41.22, 37.61[(Me2N)CꢀO], 19.33(Me2C6H3N), 11.4(C5Me5)
a, 319.38[(PhMe2CCH2)C=O], 154.93–120.72[several phenyl, C6H3Me2N,
(H5C6Me2CCH2)CꢀO], 113.33(C5Me5), 58.28 [(PhMe2CCH2)CꢀO], 38.28[(PhMe2CCH2)CꢀO],
29.71, 27.76[(PhMe2CCH2)CꢀO], 24.93(Ta–Me), 19.63(Me2C6H3N), 10.68(C5Me5)
3
3
2H, JH–H=7.5 Hz), 6.75(t, 1H, JH–H=7.5 Hz, H3C6Me2N), 3.7 [q, 2H,
2JH–H=19.5 Hz, (PhMe2CCH2)CꢀO], 2.43(s, 6H, Me2C6H3N), 1.65(s, 15H,
C5Me5), 1.40(s, 3H), 1.28[s, 3H, (PhMe2CCH2)CꢀO], 0.98(s, 3H, Ta–Me)
3
3
38
39
40
a, 7.06(d, 2H, JH–H=7.5 Hz), 6.75 (t, 1H, JH–H=7.5 Hz, H3C6Me2N), 3.43,
a, 320.66[(Me3CCH2)C=O], 131.72, 128.29, 127.32, 120.73(Ci, Co, Cm, Cp, C6H3Me2N),
113.31(C5Me5), 57.48[(Me3CCH2)CꢀO], 31.86[(Me3CCH2)CꢀO], 29.75[(Me3CCH2)CꢀO],
24.76(Ta–Me), 19.66(Me2C6H3N), 10.78(C5Me5)
a, 153.23[(Me3CCH2)CO], 132.43, 128.29, 127.3, 122.22(Ci, Co, Cm, Cp, C6H3Me2N), 116.05
(C5Me5), 57.53[(Me3CCH2)CO], 31.87[(Me3CCH2)CO], 29.56[(Me3CCH2)CO],
19.62(Me2C6H3N), 11.02(C5Me5)
a, 155.38[{H4C6(2-CH2NMe2)}CO], 147.4–119.53[several phenyl, C6H3Me2N, {H4C6(2-
CH2NMe2)}CO], 113.19(C5Me5), 66.49[{H4C6(2-CH2NMe2)}CO], 45.59[br, {H4C6(2-
CH2NMe2)}CO], 19.8(br,Me2C6H3N), 18.83(Ta–Me), 11.18(C5Me5)
2
3.06[AB, 2H, JH–H=19 Hz, (Me3CCH2)CꢀO], 2.44(s, 6H, Me2C6H3N), 1.72(s,
5
15H,C5Me5), 1.06(s, 3H, Ta–Me), 0.94[s, 9H, (Me3CCH2)CꢀO]
3
3
0
a, 6.98(d, 2H, JH–2H=7.2 Hz), 6.71 (t, 1H, JH–H=7.2 Hz, H3C6Me2N),
3.4, 2.87[AB, 2H, JH–H=20 Hz, (Me3CCH2)CO], 2.47(s, 6H, Me2C6H3N), 1.78(s,
15H, C5Me5), 0.89[s, 9H, (Me3CCH2)CO]
3
a, 7.12(d, 1H), 6.92(t, 1H), 6.70(d, 1H), 6.63[d, 1H, {H4C6(2-CH2NMe2)}CO],
3
3
7.12(d, 2H, JH–H=7.5 Hz), 6.77(t, 1H, JH–H=7.5 Hz, H3C6Me2N), 3.22,
2
3.00[AB, 2H, JH–H=13.5 Hz, {H4C6(2-CH2NMe2)}CO], 2.53[s, br, 6H,
{H4C6(2-CH2NMe2)}CO], 2.17 (s, br, 6H, Me2C6H3N), 2.03(s, 15H, C5Me5),
0.53(s, 3H, Ta–Me)
41
42
a, 6.87(m, 2H), 6.81[m, 1H, (Me3CCH2)CꢀNC6H3Me2], 2.74[q, 2H,
2JH–H=12.82 Hz, (Me3CCH2)CꢀNC6H3Me2], 2.58(s, 3H), 1.54[s, 3H,
(Me3CCH2)CꢀNC6H3Me2], 2.01(s, 15H, C5Me5), 0.95[(Me3CCH2)CꢀNC6H3Me2]
a, 240.49[(Me3CCH2)C=NC6H3Me2], 140[Ci, (Me3CCH2)CꢀNC6H3Me2], 133.85, 129.72,
128.58, 127.46, 127.12[(Me3CCH2)CꢀNC6H3Me2], 117.44(C5Me5),
47.68[(Me3CCH2)CꢀNC6H3Me2], 34.06[(Me3CCH2)CꢀNC6H3Me2], 30.54
[(Me3CCH2)CꢀNC6H3Me2], 19.22, 18.83[(Me3CCH2)CꢀNC6H3Me2], 11.53(C5Me5)
a, 235.9[(Ph)C=NC6H3Me2], 182.36–125.49[several phenyl, (H5C6)CꢀNC6H3Me2, Ta–C6H5],
116(C5Me5), 18.64, 18.31[(Ph)CꢀNC6H3Me2], 11.65(C5Me5)
a, 7.94(d, 2H), 7.78(br, 2H), 7.21(t, 2H), 7.05(m, 2H), 6.97[m, 2H,
3
(H5C6)CꢀNC6H3Me2, Ta–C6H5], 6.94(d, 1H, JH–H=7.5 Hz), 6.81(t, 1H,
3
3JH–H=7.5 Hz), 6.52[d, 1H, JH–H=7.5 Hz, (Ph)CꢀNC6H3Me2],
2.00(s, 15H, C5Me5), 2.04(s, 3H), 1.74[s, 3H, (Ph)CꢀNC6H3Me2]
a Chemical shifts in l: a, benzene-d6; b, chloroform-d.
b The most relevant shifts.

44
A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
aryl ligand s-bonded to metal centre with non-coordi-
nated amine functionality.
2.1.1. X-ray structures of [MCpCl(NAr){p2-
C(Me)ꢀNAr)}] (Ar=2,6-Me2C6H3; M=Nb,
Cp=p5-C5H4SiMe3, 1; M=Ta, Cp=p5-C5Me5, 7)
The molecular structure of compound 1 is shown in
Fig. 1 while 7 is in Fig. 2. Selected bond distances and
angles are presented in Tables 3 and 4, respectively.
Both compounds are monomers, and show the metal
centres within a classical four-legged stool environment,
or three-legged if we take into consideration the cen-
troid of the N(1)–C(21) and N(1)–C(2) bonds. The
distances for both metal centres, niobium [20] and
tantalum [5,13c,21] to the cyclopentadienyl ring car-
bons and the internal cyclopentadienyl parameters are
in the normal range. Distances from the metal centres
to the imido nitrogen atom, Nb(1)–N(2) 1.781(2) and
Scheme 3.
tively, however in the h2-iminocarbamoyl complexes
are observed at l 200.23 (13) and 199.69 (30). The
shielding of these resonances is due to the positive
charge deslocalisation between two nitrogen atoms in
h2-iminocarbamoyl complexes in agreement with the
major participation of the resonance forms II and
III (Scheme 3), proposed by Chisholm et al. [18] in
order to explain the result obtained in the insertion
process of 2,6-Me2C6H3NC into Mo–NMe2 bonds of
1
Mo(NMe2)4. Finally, the H- and 13C{1H}-NMR spec-
,
Ta(1)–N(2) 1.795(6) A are similar to other imido
tra of the complexes 12 and 29, which contain the
2-[(dimethylamino)methyl)]phenyl ligand, able to form
cyclometalated species via coordination of the nitrogen
atom to the metal centre [19], show the equivalence of
methyl groups in the NMe2 moiety, consistent with an
derivatives found in the literature [4a,5,20b]. Distances
and angles around the carbon and nitrogen atoms of
the iminoacyl groups are typical of carbon–nitrogen
double bond [N(1)–C(21) 1.265(3) for 1, N(1)–C(2)
Fig. 1. Molecular structure and atom labelling scheme for complex [Nb(h5-C5H4SiMe3)Cl(NAr){h2-C(Me)ꢀNAr}] (Ar=2,6-Me2C6H3, 1).

A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
45
Fig. 2. Molecular structure and atom labelling scheme for complex [Ta(h5-C5Me5)Cl(NAr){h2-C(Me)ꢀNAr}] (Ar=2,6-Me2C6H3, 7).
40) are easily obtained when the corresponding chloro or
methyl alkyl imido complex react with CO (1 atm) at r.t.
in n-hexane (Scheme 5). This reaction takes place by
intermolecular coupling between two acyl carbon atoms
of the unstable intermediate h2-acyl complexes
‘[TaCp*X(NAr){h2-C(R)ꢀO}]’, which could not be ob-
served when the reaction was followed by 1H-NMR
spectroscopy. However, for X=R=Me [5] we have
observed the formation of the intermediate h2-acyl
complex [TaCp*Me(NAr){h2-C(Me)ꢀO}] when the reac-
tion is followed by NMR spectroscopy at low tempera-
ture.
1.273 for 7 [22] and their bond lengths and angles with
the metal centres confirm the h2-coordination.
2.2. Reactions with carbon monoxide
Dialkyl, alkyl chloro and alkyl methyl imido tantalum
complexes [TaCp*XR(NAr)] react with carbon monox-
ide (1 atm) at r.t. in n-hexane or benzene-d6 (NMR tube)
to give alkyl h2-acyl [TaCp*X(NAr){h2-C(R)ꢀO}]
(Ar=2,6-Me2C6H3; X=R=CH2SiMe3, 31; CH2-
CMe2Ph, 32; CH2CMe3, 33; CH2Ph, 34), chloro h2-acyl
and h2-carbamoyl (X=Cl, R=CH2CMe2Ph, 35; NMe2,
36) and methyl h2-acyl (X=Me, R=CH2CMe2Ph, 37;
CH2CMe3, 38) complexes, as result of simple migration
of alkyl group bonded to the metal to the electrophilic
carbonyl atom (Scheme 4), of the previously coordinated
CO.
Table 3
a
,
Selected bond lengths (A) and angles (°) for complex 1
Bond lengths
Nb(1)–N(2)
Nb(1)–N(1)
N(1)–C(21)
N(2)–C(31)
1.781(2)
2.166(2)
1.265(3)
1.394(3)
Nb(1)–C(21)
Nb(1)–Cl(1)
N(1)–C(23)
Nb(1)–Cp(1)
2.132(3)
2.447(1)
1.428(3)
2.153
The regioselective synthesis of the methyl h2-acyl
complexes 37 and 38 reflects the preferential migration
of CH2CMe2Ph and CH2CMe3 groups according with
the sequence established for the isocyanide insertion
process.
Bond angles
N(2)–Nb(1)–C(21)
N(2)–Nb(1)–Cl(1)
N(1)–Nb(1)–Cl(1)
C(21)–N(1)–Nb(1)
C(31)–N(2)–Nb(1)
C(22)–C(21)–Nb(1) 155.7(2)
Cp(1)–Nb(1)–N(1) 126.6
Cp(1)–Nb(1)–C(21) 107.4
97.17(10) N(2)–Nb(1)–N(1)
103.14(9)
102.24(7)
85.17(6)
C(21)–Nb(1)–Cl(1) 119.26(8)
C(21)–N(1)–C(23) 131.6(2)
By this procedure, alkyl h2-acyl derivatives with X=
Cl, R=CH2CMe3; X=Me, R=2-(CH2NMe2)C6H4
cannot be isolated or detected by 1H-NMR spectroscopy
probably due to their very low stability; however, dinu-
clear ene diolate complexes [{TaCp*X(NAr)}2-
{m-h2-OC(R)ꢀC(R)O}] (Ar=2,6-Me2C6H3; X=Cl,
R=CH2CMe3, 39; X=Me, R=2-(CH2NMe2)C6H4,
71.43(16) C(23)–N(1)–Nb(1) 156.74(17)
175.35(19) N(1)–C(21)–C(22) 129.9(3)
Cp(1)–Nb(1)–Cl(1) 109.5
Cp(1)–Nb(1)–N(2) 121.7
a Cp(1) is the centroid of the C(11)–C(15) cyclopentadienyl ring.

46
A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
In the cases X=Cl, R=CH2SiMe3, CH2Ph, Ph and
Table 4
a
,
Selected bond lengths (A) and angles (°) for complex 7
X=Me, R=CH2SiMe3, CH2Ph, Ph the reaction with
CO takes place but leads to an unidentified mixture of
products, whereas for X=Cl, R=2-(CH2NMe2)C6H4
there is no reaction even on heating at 100°C.
All of the complexes 31–42 are soluble in aromatic
and chlorinated solvents and partially soluble in satu-
rated hydrocarbons.
Bond lengths
Ta(1)–N(2)
Ta(1)–N(1)
N(1)–C(2)
N(2)–C(21)
Ta(1)–Cp*(1)
1.795(6)
2.139(6)
1.273(9)
1.382(11)
2.142
Ta(1)–C(2)
Ta(1)–Cl(1)
N(1)–C(11)
C(2)–C(3)
2.137(7)
2.427(2)
1.443(9)
1.490(10)
1
The analytical (Section 3), IR (Table 1) and H- and
Bond angles
13C{1H}-NMR (Table 2) spectroscopic data for com-
pounds 31–42 are consistent with their formulation. All
the complexes show the characteristic absorption for
the pentamethylcyclopentadienyl ring (nC–C:1028
cm−1) [11]. The imido h2-acyl complexes 31–38 show
the wTaꢀN [15] and wC(R)ꢀO [23] at :1327 and 1589
cm−1, respectively. The CꢀO stretching vibration in
h2-acyls ranges from 1453 to 1625 cm−1 and the lowest
stretching frequencies occur for h2-acyl complexes con-
taining high-valent metals, as in our case. This has been
attributed to the participation of a ‘carbene-like’ reso-
nance form [24] or to the contribution of a ‘carbenium
ion like’ acceptor orbital on the undistorted h2-acyl
structure [25].
Their NMR data accord with the expected pseudo-
square-pyramidal structure with chiral metal atoms.
The h2-acyl carbon resonance appears at l:317 but
the corresponding to the h2-carbamoyl derivative 36 is
shifted to higher field at l 228, in the typical ranges for
h2-acyl [26] and h2-carbamoyl [27] complexes. Further,
the 1H-NMR spectrum of the h2-carbamoyl complex 36
exhibits inequivalent methyl groups due to the slow
rotation around the Cacyl–NMe2 bond [10,18,27,28] like
the organic amides.
N(2)–Ta(1)–C(2)
C(2)–Ta(1)–N(1)
C(2)–Ta(1)–Cl(1)
C(2)–N(1)–C(11)
C(11)–N(1)–Ta(1) 155.0(5)
N(1)–C(2)–C(3) 126.5(7)
99.5(3)
34.7(2)
118.2(2)
131.8(6)
N(2)–Ta(1)–N(1)
N(2)–Ta(1)–Cl(1)
N(1)–Ta(1)–Cl(1)
C(2)–N(1)–Ta(1)
C(21)–N(2)–Ta(1) 170.2(6)
C(3)–C(2)–Ta(1) 160.6(6)
104.3(3)
102.6(2)
83.90(17)
72.6(4)
Cp*(1)–Ta(1)–N(1) 131.6
Cp*(1)–Ta(1)–Cl(1) 108.6
Cp*(1)–Ta(1)–N(2) 117.2
Cp*(1)–Ta(1)–C(2) 110.7
a Cp*(1) is the centroid of the C(31)–C(35) pentamethylcyclopenta-
dienyl ring.
When the same reaction with CO was carried out
using [TaCp*XR(NAr)] (Ar=2,6-Me2C6H3; X=Cl,
R=CH2CMe3; X=R=Ph) as starting materials the
expected imido h2-acyl derivatives were not obtained,
since they were spontaneously converted into the oxo
h2-iminoacyl complexes [TaCp*X(O){h2-C(R)ꢀNAr}]
after 35 days (X=Cl, R=CH2CMe3, 41) and 12 h
(X=R=Ph, 42), respectively (Scheme 5). The forma-
tion of complexes 41–42 can be explained assuming
three steps: (a) the initial formation of non-stable h2-
acyl complex, (b) a nucleophilic attack of the imido
nitrogen atom at the electrophilic acyl carbon atom
leads to an unidentified intermediate and (c) sponta-
neous rearrangement, by the rupture of the C–O single
bond and simultaneous formation of the TaꢀO double
bond to give the final oxo h2-iminoacyl complexes
41–42, as we have proposed for similar methyl tanta-
lum derivatives [5].
The ene diolate complexes 39 and 40 show wCꢀC [2b,d,
29], wTaꢀN [17], wC-O [29a] and wTa–O [16a] IR absorptions
at :1587, 1332, 1159 and 812 cm−1, respectively,
whereas the oxo h2-iminoacyl complexes 41 and 42
show the wC(R)ꢀN [14] and wTaꢀO [29c, 30] IR absorptions
at 1601 and 901 cm−1, respectively. In addition, its
NMR spectra demonstrate all expected signals.
Scheme 4.

A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
47
Scheme 5.
2.3. Concluding remarks
2.2.1. X-ray structure of [TaCp*Me(NAr)-
{p2-C(CH2CMe2Ph)ꢀO}] (Ar=2,6-Me2C6H3, 37)
The molecular structure and atom-labelling scheme
of 37 are shown in Fig. 3, while relevant geometrical
parameters are summarised in Table 5. Compound 37
can be described as a monomer with the typical four-
legged piano stool environment for the tantalum
atom, where the four legs are occupied by the imido,
methyl and the carbon and oxygen atoms of acyl
group. Bond lengths and angles between the pen-
tamethylcyclopentadienyl ring and the tantalum atom
are in the normal range [2,5,21]. In relation with the
With this work we have completed a systematic study
of the isocyanide and carbon monoxide insertion reac-
tions into metal–carbon bonds of different alkyl imido
cyclopentadienyl niobium and tantalum complexes. Sta-
ble 18-electron h2-iminoacyl compounds [MCpX-
(NAr){h2-C(R)ꢀNAr}] (1–18) are obtained by insertion
of 2,6-Me2C6H3NC into M–C(alkyl) bonds of alkyl
chloro or dialkyl imido complexes MCpXR(NAr). In
contrast, the reaction with alkyl methyl imido tantalum
complexes takes place with migration of alkyl or methyl
group to give mixture of methyl h2-alkyliminoacyl
[TaCp*Me(NAr){h2-C(R)ꢀNAr}] (19, 21, 23, 25, 27,
29, 30) and alkyl h2-methyliminoacyl [TaCp*R-
(NAr){h2-C(Me)ꢀNAr}] (20, 22, 24, 26, 28) derivatives,
respectively. In the cases of the starting 2-[(di-
methylamino)methyl]phenyl methyl and dimethyl-
amido methyl imido complexes the insertion reac-
tions take place with a regioselective migration of the
2-[(dimethylamino)methyl]phenyl and dimethylamido
groups. Reactions of the alkyl imido tantalum(V)
complexes with CO occur through the formation of the
expected alkyl h2-acyl (31–34), chloro h2-acyl (35, 36)
and methyl h2-acyl (37, 38) [TaCp*X(NAr){h2-
,
imido disposition, the Ta(1)–N(1) [1.815(11) A] bond
distance is similar to that found in 7 and the Ta(1)–
N(1)–C(21) [172.2(10)°] angle is in the range of linear
imido ligands [4a,5].
On the other hand, the bonding system between the
acyl group and the tantalum is very similar to that
found in [TaCp*Cl3{h2-C(CH2CMe3)ꢀO}] [29c]. How-
,
ever, the Ta(1)–C(31) [2.126(14) A] and Ta(1)–O(1)
,
[2.214(11) A] bond lengths are slightly longer than the
corresponding in the trichloride derivative, due to the
existing difference between the donor ability and trans
effect of the chloride and imide ligands.

48
A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
Fig. 3. Molecular structure and atom labelling scheme for complex [Ta(h5-C5Me5)Me(NAr){h2-C(CH2CMe2Ph)ꢀO}] (Ar=2,6-Me2C6H3, 37).
Table 5
C(R)ꢀO}] compounds, respectively, but lead to differ-
a
,
Selected bond lengths (A) and angles (°) for complex 37
ent products depending on X. The higher carbenoid
character of the acyl ligand when X=Cl, R=
CH2CMe3 and X=Me, R=2-(CH2NMe2)C6H4, leads
to the dinuclear ene diolate complexes [{TaCp*X-
(NAr)}2{m-h2-OC(R)=C(R)O}] (39, 40), whereas the
nucleophilic attack of the imido nitrogen at the elec-
trophilic acyl carbon atom when X=Cl, R=
CH2CMe3 and X=R=Ph after long reaction times
finally gives the oxo h2-iminoacyl complexes
[TaCp*X(O){h2-C(R)ꢀNAr}] (41, 42).
Bond lengths
Ta(1)–N(1)
Ta(1)–O(1)
O(1)–C(31)
Ta(1)–Cp*(1)
1.815(11)
2.214(11)
1.240(16)
2.124
Ta(1)–C(31)
Ta(1)–C(1)
C(31)–C(32)
2.126(14)
2.220(14)
1.490(19)
Bond angles
N(1)–Ta(1)–C(31) 101.4(5)
C(31)–Ta(1)–O(1) 33.1(4)
C(31)–Ta(1)–C(1) 110.6(6)
C(21)–N(1)–Ta(1) 172.2(10)
O(1)–C(31)–Ta(1)
N(1)–Ta(1)–O(1)
N(1)–Ta(1)–C(1)
O(1)–Ta(1)–C(1)
O(1)–C(31)–C(32)
C(32)–C(31)–Ta(1)
Cp*(1)–Ta(1)–O(1)
Cp*(1)–Ta(1)–C(31)
105.1(5)
100.6(6)
77.6(5)
123.1(12)
159.4(10)
128.7
77.3(9)
Cp*(1)–Ta(1)–N(1) 121.2
Cp*(1)–Ta(1)–C(1) 111.3
110.9
3. Experimental
a Cp*(1) is the centroid of the C(11)–C(15) pentamethylcyclopenta-
dienyl ring.
3.1. General considerations
All reactions and manipulations were carried out
under an atmosphere of argon using standard Schlenk-
tube and cannula techniques or in a conventional ar-
gon-filled glove-box. Solvents were refluxed over an
appropriate drying agent and distilled and degassed
prior to use: chloroform-d (NaH), benzene-d6 and n-
hexane (Na–K alloy). Literature methods were em-
ployed for the synthesis of starting materials
MCpXR(NAr) (Ar=2,6-Me2C6H3; M=Nb, Cp=h5-
C5H4SiMe3=Cp%, X=Cl, R=Me [4e]; X=Me, R=
Me [4e], NMe2 [4e]; M=Ta, Cp=h5-C5Me5=Cp*,
X=Cl, R=Me [5], NMe2 [4e], CH2SiMe3 [4d],
CH2CMe2Ph [4d], CH2CMe3 [4d], CH2C6H5 [4d], 2-
(CH2NMe2)C6H4 [4d]; X=Me, R=NMe2 [4e],
CH2SiMe3 [4d], CH2CMe2Ph [4d], CH2CMe3 [4d],
CH2C6H5 [4d], C6H5 [4d], 2-(CH2NMe2)C6H4 [4d]; X=
R=CH2SiMe3 [4d], CH2CMe2Ph [4d], CH2CMe3 [4d],
CH2C6H5 [4d], C6H5 [4d]). Reagents were purchased
from commercial sources and used without further
purification as follows: 2,6-Me2C6H3NC (Aldrich) and
CO (Air Liquide).
Infrared spectra were recorded on a Perkin–Elmer
583 spectrophotometer (4000–200 cm−1) as Nujol
mulls between CsI or polyethylene pellets. 1H- and
13C{1H}-NMR spectra were recorded on Varian Unity
300 and Varian Unity 500 Plus spectrometers and
1
chemical shifts were measured relative to residual H
and 13C resonances in the deuterated solvents C6D6(l
7.15), CDCl3(l 7.24) and C6D6(l 128), CDCl3(l 77),
respectively. C, H and N analyses were carried out with
a Perkin–Elmer 240C microanalyzer.

A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
49
3.2. Synthesis of [NbCp%X{N(2,6-Me2C6H3)}-
{p2-C(R)ꢀN(2,6-Me2C6H3)}] (X=Cl, R=Me, 1;
X=Me, R=NMe2, 2; Me, 3; X=R=CH2SiMe3, 4;
CH2CMe3, 5; CH2Ph, 6)
ane (2×5 ml), dried in vacuo and identified as com-
plexes 8–10, 12 (yellow), 11 (pale brown) and 13 (pale
yellow). The filtrate was concentrated to ca. 10 ml and
cooled to −40°C to give 8–13 as microcrystalline
solids.
A solution of CN(2,6-Me2C6H3) (1, 0.23 g, 1.75
mmol; 2, 0.22 g, 1.72 mmol; 3, 0.24 g, 1.84 mmol; 4,
0.17 g, 1.33 mmol; 5, 0.19 g, 1.42 mmol; 6, 0.17 g, 1.32
mmol) in n-hexane (15 ml) was added at r.t. to a
solution of [NbCp%XR{N(2,6-Me2C6H3)}] (0.70 g; 1,
1.75 mmol; 2, 1.72 mmol; 3, 1.84 mmol; 4, 1.33 mmol;
5, 1.42 mmol; 6, 1.32 mmol) in n-hexane (25 ml) and
the mixture was stirred for 12 h. 1 and 6 can be
separated as insoluble pale-yellow (1) and brown (6)
microcrystalline solids, whereas in the other cases, the
resulting solution was filtered, concentrated to ca. 10 ml
and cooled to −40°C to give the h2-iminoacyl
derivates as brown (2, 4, 5) and orange(3) crystals.
The data for 1 follow. Yield 0.70 g (85%). Anal.
Found: C, 59.13; H, 6.50; N, 5.19. C26H34ClN2SiNb.
Calc.: C, 58.83; H, 6.41; N, 5.28%.
The data for 8 follow. Yield 0.40 g (80%). Anal.
Found: C, 56.18; H, 6.46; N, 4.20. C31H44ClN2SiTa.
Cal.: C, 56.31; H, 6.71; N, 4.24%.
The data for 9 follow. Yield 0.48 g (80%). Anal.
Found: C, 60.39; H, 6.45; N, 3.98. C37H46ClN2Ta.
Calc.: C, 60.45; H, 6.30; N, 3.81%.
The data for 10 follow. Yield 0.49 g (80%). Anal.
Found: C, 56.93; H, 6.55; N, 4.23. C32H44ClN2Ta.
Calc.: C, 57.10; H, 6.59; N, 4.16%.
The data for 11 follow. Yield 0.49 g (80%). Anal.
Found: C, 58.45; H, 5.95; N, 4.12. C34H40ClN2Ta.
Calc.: C, 58.92; H, 5.82; N, 4.04%.
The data for 12 follow. Yield 0.39 g (80%). Anal.
Found: C, 58.89; H, 5.81; N, 5.71. C36H45ClN3Ta.
Calc.: C, 58.77; H, 6.16; N, 5.71%.
The data for 13 follow. Yield 0.50 g (80%). Anal.
Found: C, 53.86; H, 6.18; N, 6.47. C29H39ClN3Ta.
Calc.: C, 53.91; H, 6.08; N, 6.50%.
The data for 2 follow. Yield 0.39 g (42%). Anal.
Found: C, 62.11; H, 7.40; N, 7.78. C28H40N3SiNb.
Calc.: C, 62.35; H, 7.42; N, 7.68%.
The data for 3 follow. Yield 0.65 g (70%). Anal.
Found: C, 63.41; H, 7.25; H, 5.47. C27H37N2SiNb.
Calc.: C, 63.51; H, 7.30; N, 5.49%.
Tha data for 4 follow. Yield 0.65 g (75%). Anal.
Found: C, 59.71; H, 8.25; N, 4.29. C32H53N2Si3Nb.
Calc.: C, 59.78; H, 8.31; N, 4.36%.
The data for 5 follow. Yield 0.66 g (75%). Anal.
Found: C, 66.76; H, 8.69; N, 5.02. C34H53N2SiNb.
Calc.: C, 66.86; H, 8.75; N, 4.59%.
The data for 6 follow. Yield 0.76 g (85%). Anal.
Found: C, 69.84; H, 6.90; N, 4.27. C39H45N2SiNb.
Calc.: C, 70.70; H, 6.80; N, 4.23%.
3.4. Synthesis of [TaCp*R(NAr){p2-C(R)ꢀNAr}]
(Ar=2,6-Me2C6H3; R=CH2SiMe3, 14; CH2-
CMe2Ph, 15; CH2CMe3, 16; CH2C6H5, 17; C6H5, 18)
A stirred solution of [TaCp*R2(NAr)] (0.50 g; R=
CH2SiMe3, 0.82 mmol; CH2CMe2Ph, 0.71 mmol;
CH2CMe3, 0.86 mmol; CH2C6H5, 0.81 mmol; C6H5,
0.77 mmol), in n-hexane (30 ml) was treated with
ArNC (R=CH2SiMe3, 0.107 g; CH2CMe2Ph, 0.09 g;
CH2CMe3, 0.11 g; CH2C6H5, 0.106 g; C6H5, 0.109 g) in
a 1:1 molar ratio and under rigorously anhydrous
conditions for 6 h. Complexes 14–18 were obtained as
precipitates and then separated by filtration. The solu-
tion was concentrated to ca. 10 ml and cooled to
−40°C to give 14, 15 (pale brown), 16, 17 (yellow) and
18 (orange) microcrystalline solids.
3.3. Synthesis of [TaCp*Cl(NAr){p2-C(R)ꢀNAr}]
(Ar=2,6-Me2C6H3; R=CH2SiMe3, 8; CH2CMe2Ph,
9; CH2CMe3, 10; CH2C6H5, 11; 2-(CH2NMe2)C6H4,
12; NMe2, 13)
The data for 14 follow. Yield 0.48 g (80%). Anal.
Found: C, 56.65; H, 7.38; N, 3.71. C35H55N2Si2Ta.
Calc.: C, 56.73; H, 7.48; N, 3.78%.
The data for 15 follow. 0.47 g (80%). Anal. Found:
C, 67.68; H, 7.04; N, 3.26. C47H59N2Ta. Calc.: C, 67.77;
H, 7.14; N, 3.36%.
The data for 16 follow. Yield 0.49 g (80%). Anal.
Found: C, 62.60; H, 7.74; N, 3.84. C37H55N2Ta. Calc.:
C, 62.70; H, 7.82; N, 3.95%.
The data for 17 follow. Yield 0.48 g (80%). Anal.
Found: C, 65.63; H, 6.22; N, 3.62. C41H47N2Ta. Calc.:
C, 65.76; H, 6.32; N, 3.74%.
A
sample of [TaCp*ClR(NAr)] (0.50 g; R=
CH2SiMe3, 0.76 mmol; CH2CMe2Ph, 0.82 mmol;
CH2CMe3, 0.92 mmol; CH2C6H5, 0.89 mmol; 2-
(CH2NMe2)C6H4, 0.82 mmol; NMe2, 0.97 mmol) was
dissolved in 25 ml of n-hexane in a Schlenk tube. After
addition of a n-hexane (10 ml) solution of isocyanide
ArNC (R=CH2SiMe3, 0.10 g, 0.76 mmol;
CH2CMe2Ph, 0.11 g, 0.82 mmol; CH2CMe3, 0.12 g,
0.92 mmol; CH2C6H5, 0.116 g, 0.89 mmol; 2-
(CH2NMe2)C6H4, 0.11 g, 0.82 mmol; NMe2, 0.127 g,
0.97 mmol) the colour of the mixture changed quickly
to yellow. The reaction mixture was stirred for 6 h at
r.t. and then the resulting suspension was decanted and
filtered. The residual solid was washed with cold n-hex-
The data for 18 follow. Yield 0.44 g (80%). Anal.
Found: C, 65.24; H, 5.94; N, 4.02. C39H43N2Ta. Calc.:
C, 65.00; H, 6.01; N, 3.89%.

50
A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
3.5. Synthesis of [TaCp*Me(NAr){p2-C(R)ꢀNAr}] and
[TaCp*R(NAr){p2-C(Me)ꢀNAr}] (Ar=2,6-Me2C6H3;
R=CH2SiMe3, 19; CH2C6H5, 21 and R=CH2SiMe3,
20; CH2C6H5, 22)
The data for 25 follow. Yield 0.48 g (77%). Anal.
Found: C, 60.68; H, 7.21; N, 4.32. C33H47N2Ta. Calc.:
C, 60.73; H, 7.26; N, 4.29%.
The data for 27 follow. Yield 0.43 g (70%). Anal.
Found: C, 61.96; H, 6.22; N, 4.35. C34H41N2Ta. Calc.:
C, 62.00; H, 6.27; N, 4.25%.
3.5.1. Method A
A solution of isocyanide 2.6-Me2C6H3NC (0.12 g,
0.92 mmol) in n-hexane (15 ml) was added at r.t. to a
yellow solution of [TaCp*RMe(NAr)] (0.50 g; R=
CH2SiMe3, 0.93 mmol; CH2C6H5, 0.923 mmol) in n-
hexane (25 ml) and stirred for 6 h. The resulting yellow
suspension was decanted, filtered, the yellow microcrys-
talline solids washed twice with cold n-hexane (2×5
ml) and identified as 20 and 22.
The data for 20 follow. Yield 0.43 g (70%). Anal.
Found: C, 57.57; H, 6.89; N, 3.09. C32H47N2SiTa.
Calc.: C, 57.47; H, 7.08; H, 4.19%.
The data for 22 follow. Yield 0.49 g (80%). Anal.
Found: C, 62.29; H, 6.60; N, 4.09. C47H43N2Ta. Calc.:
C, 62.49; H, 6.44; N, 4.16%.
The data for 29 follow. Yield 0.54 g (90%). Anal.
Found: C, 61.82; H, 6.86; N, 5.88. C37H48N3Ta. Calc.:
C, 62.09; H, 6.76; N, 5.87%.
The data for 30 follow. Yield 0.53 g (85%). Anal.
Found: C, 57.49; H, 6.59; N, 6.66. C30H42N3Ta. Calc.:
C, 57.59; H, 6.76; N, 6.71%.
3.6.2. Method B
In
a
standard experiment,
a
solution of
[TaCp*RMe(NAr)] (0.25 g; R=CH2CMe2Ph, 0.425
mmol; CH2CMe3, 0.48 mmol; C6H5, 0.47 mmol; 2-
(CH2NMe2)C6H4, 0.425 mmol; NMe2, 0.5 mmol) in 0.8
ml of benzene-d6 was prepared and transfered to a
valved NMR tube containing an equimolar amount of
isocyanide 2,6-Me2C6H3NC (R=CH2CMe2Ph, 0.055g;
CH2CMe3, 0.063 g; C6H5, 0.0615 g; 2-(CH2NMe2)C6H4,
0.055 g; NMe2, 0.065 g). The solution was shaken until
3.5.2. Method B
In a typical experiment [TaCp*RMe(NAr)] (0.25 g;
R=CH2SiMe3, 0.465 mmol; CH2C6H5, 0.4612 mmol),
ArNC (0.06 g, 0.46 mmol) and benzene-d6 (0.7 ml) were
placed in a valved NMR tube. The reaction was moni-
1
homogeneous and the reaction monitored by H-NMR
spectroscopy until total conversion of the tantalum
starting complex to the h2-iminoacyl complexes 23–30.
The yield was determined from sealed NMR tube reac-
tions; R=CH2CMe2Ph, 23, 75%; 24, 25%; CH2CMe3,
25, 77%; 26, 23%; C6H5, 27, 70%; 28, 30%; 2-
(CH2NMe2)C6H4, 29, 100%; NMe2, 30, 100%.
When the yellow suspension obtained by method A
was evaporated to dryness, a 1H-NMR spectrum in
benzene-d6 of the crude residue gave the same result.
1
tored by H-NMR spectroscopy until the starting mate-
rial was totally transformed and no further change was
observed. The formation of the corresponding h2-imi-
noacyl complexes 19–22 was confirmed by their 1H-
NMR spectrum. Yield: R=CH2SiMe3, 19, 30%; 20,
70%; CH2C6H5, 21, 20%; 22, 80%.
When the yellow suspension obtained by method A
was evaporated to dryness, a 1H-NMR spectrum in
benzene-d6 of the crude residue gave the same result.
3.6. Synthesis of [TaCp*Me(NAr){p2-C(R)ꢀNAr}] and
[TaCp*R(NAr){p2-C(Me)ꢀNAr}] (Ar=2,6-Me2C6H3,
R=CH2CMe2Ph, 23; CH2CMe3, 25; C6H5, 27;
2-(CH2NMe2)C6H4, 29; NMe2, 30 and
3.7. Synthesis of [TaCp*X(NAr){p2-C(R)ꢀO}] (Ar=
2,6-Me2C6H3; X=R=CH2SiMe3, 31; CH2CMe2Ph,
32; CH2CMe3, 33; CH2Ph, 34)
R=CH2CMe2Ph, 24; CH2CMe3, 26; C6H5, 28)
3.7.1. Method A
An n-hexane (35 ml) solution of [TaCp*XR(NAr)]
(0.50 g; X=R=CH2SiMe3, 0.82 mmol; CH2CMe2Ph,
0.71 mmol; CH2CMe3, 0.86 mmol) was placed into a
Schlenk tube under a CO atmosphere (1 atm) and the
mixture then was stirred at r.t. for 12 (X=R=
CH2SiMe3), 24 (X=R=CH2CMe2Ph) and 72 (X=
R=CH2CMe3) h. The resulting suspension was
evaporated to dryness and the residue extracted into
n-hexane (2×15 ml). The solution was filtered, concen-
trated to ca. 10 ml and cooled to −40°C to give 31–33
as deep-yellow (31), pale-brown (32) and brown (33)
microcrystalline solids.
3.6.1. Method A
The mixed alkyl imido complex [TaCp*RMe(NAr)]
(0.50 g; R=CH2CMe2Ph, 0.85 mmol; CH2CMe3, 0.96
mmol; C6H5, 0.94 mmol; 2-(CH2NMe2)C6H4, 0.85
mmol; NMe2, 1 mmol) was dissolved in 25 ml of
n-hexane and isocyanide 2,6-Me2C6H3NC (R=
CH2CMe2Ph, 0.11 g; CH2CMe3, 0.126 g; C6H5, 0.123 g;
2-(CH2NMe2)C6H4, 0.11 g; NMe2, 0.13 g) in an 1:1
molar ratio was added. The solution was stirred and the
yellow (23, 25, 27, 29) or beige (30) microcrystalline
solids formed after 6 h, were collected by decanting the
solvent and washing with 5 ml of cold n-hexane.
The data for 23 follow. Yield 0.45 g (75%). Anal.
Found: C, 63.71; H, 7.03; N, 3.88. C38H49N2Ta. Calc.:
C, 63.86; H, 6.91; N, 3.92%.
The data for 31 follow. Yield 0.35 g (75%). Anal.
Found: C, 55.56; H, 7.77; N, 2.28. C27H46ONSi2Ta.
Calc.: C, 55.76; H, 7.97; N, 2.41%.

A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
51
The data for 32 follow. Yield 0.36 g (70%). Anal.
Found: C, 64.05; H, 6.86; N, 1.86. C39H50ONTa. Calc.:
C, 64.18; H, 6.90; N, 1.92%.
The data for 33 follow. Yield 0.36 g (70%). Anal.
Found: C, 57.41; H, 7.59; N, 2.27. C29H46ONTa. Calc.:
C, 57.51; H, 7.65; N, 2.31%.
charged into a Schlenk tube under rigorously anhy-
drous conditions. The argon atmosphere was replaced
by CO (1 atm) and the solution stirred for 12 h. From
the resulting yellow suspension microcrystalline solids
were collected by filtration, dried in vacuo and iden-
tified as 39 and 40.
The data for 39 follow. Yield 0.39 g (80%). Anal.
Found: C, 50.47; H, 6.21; N, 2.48. C48H70O2Cl2N2Ta.
Calc.: C, 50.58; H, 6.19; N, 2.46%.
The data for 40 follow. Yield 0.41 g (80%). Anal.
Found: C, 56.71; H, 6.53; N, 4.47. C58H78O2N4Ta.
Calc.: C, 56.86; H, 6.42; N, 4.57%.
3.7.2. Method B
A benzene-d6 (0.6 ml) solution of [TaCp*XR(NAr)]
(X=R=CH2Ph, 0.125 g, 0.20 mmol) was placed in a
NMR tube under a CO atmosphere (1 atm) and then
the tube flame sealed. The yellow colour of the mixture
no changed, but the reaction was instantaneous and
monitored by 1H-NMR spectroscopy confirmed the
complete conversion of the dibenzyl imido complex into
34.
3.10. Synthesis of [TaCp*Cl(O){p2-
C(CH2CMe3)ꢀNAr}] (Ar=2,6-Me2C6H3, 41)
In a NMR tube, a benzene-d6 (0.7 ml) solution of
[TaCp*Cl(CH2CMe3)(NAr)] (0.16 g, 0.28 mmol) was
placed and the argon atmosphere replaced by CO (1
atm). The NMR tube was sealed and the reaction
monitored by NMR spectroscopy at r.t. After 35 days
the formation of the corresponding chloro oxo h2-imi-
noacyl complex 41 was confirmed by their 1H- and
13C-NMR spectra.
3.8. Synthesis of [TaCp*X(NAr){p2-C(R)ꢀO}] (Ar=
2,6-Me2C6H3; X=Cl, R=CH2CMe2Ph, 35; NMe2,
36; X=Me, R=CH2CMe2Ph, 37; CH2CMe3, 38)
3.8.1. Method A
A solution of [TaCp*XR(NAr)] (0.50 g, X=Cl, R=
CH2CMe2Ph, 0.71 mmol; X=Me, R=CH2CMe2Ph,
0.85 mmol; CH2CMe3, 0.96 mmol) in n-hexane (35 ml)
was placed in an ampoule under a CO atmosphere (1
atm) and then sealed. The reaction mixture was stirred
at r.t. for 12 h. After the ampoule was opened, the
suspension evaporated to dryness and the residue re-
crystallized from n-hexane at −40°C to give 35, 37 and
38 as yellow microcrystalline solids.
The data for 35 follow. Yield 0.33 g (75%). Anal.
Found: C, 55.05; H, 5.92; N, 2.19. C29H37OClNTa.
Calc.: C, 55.11; H, 5.90; N, 2.22%.
The data for 37 follow. Yield 0.39 g (75%). Anal.
Found: C, 58.92; H, 6.22; N, 2.26. C30H40ONTa. Calc.:
C, 58.91; H, 6.59; N, 2.29%.
3.11. Synthesis of [TaCp*Ph(O){p2-C(Ph)=NAr}]
(Ar=2,6-Me2C6H3, 42)
A red–orange solution of [TaCp*Ph2(NAr)] (0.48 g,
0.74 mmol) in n-hexane (40 ml) was placed into a
Schlenk tube and the argon atmosphere replaced by
carbon monoxide (1 atm). The reaction mixture was
stirred at r.t. for 12 h and then, the resulting suspension
evaporated to dryness. The residue was recrystallized
from n-hexane to give 42 as a yellow microcrystalline
solid.
The data for 42 follow. Yield 0.35 g (75%). Anal.
Found: C, 60.22; H, 5.48; N, 2.29. C31H34ONTa. Calc.:
C, 60.29; H, 5.55; N, 2.26%.
The data for 38 follow. Yield 0.39 g (75%). Anal.
Found: C, 54.47; H, 6.89; N, 2.47. C25H38ONTa. Calc.:
C, 54.64; H, 6.97; N, 2.55%.
3.12. X-ray structure determination of compounds 1, 7
and 37
3.8.2. Method B
In a typical experiment, a CDCl3 (0.7 ml) solution of
[TaCp*Cl(NMe2)(NAr)] (0.125 g, 0.24 mmol) was
placed into a NMR tube, the argon atmosphere re-
placed by CO and the tube flame sealed. The disappear-
ance of starting tantalum complex and formation of 36
were monitored as the reaction progressed at 25°C.
Table 6 provides a summary of the crystal data, data
collection and refinement parameters for complexes 1, 7
and 37. All data were collected on an Enraf Nonius
CAD4 diffractometer at r.t. Intensity measurements
were performed by ꢀ scans in the range 6°B2qB50°
for 1, ꢀ−2q 4°B2qB50° for 7 and ꢀ−q 6°B2qB
50° for 37. Of the 5363 measured reflections for 1, 4699
were independent; R1=0.029 and wR2=0.073 (for
3846 reflections with F\4|(F)). Of the 5059 measured
reflections for 7, 4758 were independent; R1=0.037 and
wR2=0.100 (for 3740 reflections with F\4|(F)). A
total of 4910 independent reflections were measured for
37, R1=0.080 and wR2=0.171 (for 2557 reflections
3.9. Synthesis of [{TaCp*X(NAr)}2{v-p2-OC(R)ꢀ
C(R)O}] (Ar=2,6-Me2C6H3; X=Cl, R=CH2CMe3,
39; X=Me, R=2-(CH2NMe2)C6H4, 40)
A yellow solution of [TaCp*XR(NAr)] (0.50 g; X=
Cl, R=CH2CMe3, 0.86 mmol; X=Me, R=2-
(CH2NMe2)C6H4, 0.85 mmol) in n-hexane (35 ml) was

52
A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
Table 6
Crystal data and structure refinement for complexes 1, 7 and 37 a
1
7
37
Empirical formula
M
C26H34ClN2NbSi
531.00
C28H36ClN2Ta
616.99
C30H40NOTa
611.58
Crystal system; space group
Monoclinic; P21/n
10.292(3), 15.333(1), 17.256(4)
100.40(1)
2678.4(10)
4
1.317
0.609
1104
Monoclinic; P21/n
9.341(3), 24.653(4), 12.055(3)
103.40(1)
2700.5(12)
4
1.518
4.186
1232
Orthorhombic; Pbca
15.070(6), 15.859(2), 23.464(4)
,
a, b, c (A)
i (°)
3
,
U (A )
5608(3)
8
1.449
3.941
Z
Dcalc (g cm−3
)
v(Mo–Kh) (mm−1
F(000)
)
2464
Crystal size (mm)
q range for data collection (°)
Index ranges
0.48×0.44×0.38
3.14–25.03
0BhB12, 0BkB18,
−20BlB20
5363
0.48×0.45×0.38
2.39–25.16
0BhB11, 0BkB29,
−14BlB13
5059
0.38×0.34×0.27
3.03–25.03
−17BhB0, 0BkB18,
−27BlB0
4910
Reflections collected
Independent reflections
Observed reflections [I\2|(I)]
Absorption correction
Max. and min. transmission
Data/restraints/parameters
Goodness–of–fit on F2
Final R1, wR2 indices [I\2|(I)]
(all data)
4699 [Rint=0.0222]
3846
Psi scan
0.317 and 0.291
4699/0/288
1.046
0.029, 0.073
0.045, 0.078
4758 [Rint=0.0277]
4910 [Rint=0.001]
2557
Psi scan
1.000 and 0.000
4910/0/298
0.926
0.080, 0.171
0.151, 0.191
Psi scan
0.349 and 0.268
4758/0/289
1.172
0.037, 0.099
0.064, 0.120
Weighting scheme, w
Largest diff. peak, hole (e A
1/[|2(Fo2)+(0.0359P)2+1.4953P] 1/[|2(F2o)+(0.0636P)2+5.5060P] 1/[|2(F2o)+(0.1173P)2]
0.308, −0.287
−3
,
)
1.885, −2.263
1.720, −1.724
a Details in common: Mo–Kh radiation (10.71073 A); P=(Fo+2Fc)/3.
2
2
,
with F\4|(F)). The values of R1 and wR2 are defined
R1 = ꢀ ꢁꢁFoꢁ − ꢁFcꢁꢁ[ꢀ ꢁFoꢁ]; wR2 = {[ꢀ w(F2o−Fc2)2]/
[ꢀ w(Fo)2]}1/2. The structures were solved by direct
methods (SHELXS-97) and refined by least-squares
against F2 (SHELXL-97) [31].
References
[1] (a) E.J. Kulhmann, J.J. Alexander, Coord. Chem. Rev. 33 (1980)
195. (b) L.D. Durfee, I.P. Rothwell, Chem. Rev. 88 (1988) 1059.
[2] (a) P.T. Wolczanski, J.E. Bercaw, Acc. Chem. Res. 13 (1980)
121. (b) K.W. Chiu, R.A. Jones, G. Wilkinson, A.M.R. Galas,
M.B. Hursthouse, J. Am. Chem. Soc. 102 (1980) 7978. (c) M.J.
Wax, R.G. Bergman, J. Am. Chem. Soc. 103 (1981) 7028. (d)
K.W. Chiu, R.A. Jones, G. Wilkinson, A.M.R. Galas, M.B.
Hursthouse, J. Chem. Soc. Dalton Trans. (1981) 2088. (e) T.C.
Flood, in: G.L. Geoffrey (Ed.), Topics in Stereochemistry, vol.
12, Wiley, New York, 1981, p. 83. (f) J.M. Mayer, C.J. Curtis,
J.E. Bercaw, J. Am. Chem. Soc. 105 (1983) 2651. (g) W.A.
Nugent, D.W. Overall, S.J. Holmes, Organometallics 2 (1983)
161. (h) J.J. Alexander, in: F.R. Hartley (Ed.), The Chemistry of
the Metal–Carbon Bond, vol. 2, Wiley, New York, 1985. (i)
L.R. Chamberlain, I.P. Rothwell, J.C. Huffman, J. Chem. Soc.
Chem. Commun. (1986) 1203. (j) T. Sielisch, U. Behrens, J.
Organomet. Chem. 310 (1986) 179. (k) H. Brunner, J. Wachter,
J. Schmidbauer, Organometallics 5 (1986) 2212. (l) L.D. Durfee,
P.E. Fanwick, I.P. Rothwell, J. Am. Chem. Soc. 109 (1987) 4720.
(m) L.R. Chamberlain, B.D. Steffey, I.P. Rothwell, J.D. Huff-
man, Polyhedron 8 (1989) 341. (n) L.D. Durfee, J.E. Hill, P.E.
Fanwick, I.P. Rothwell, Organometallics 9 (1990) 75.
4. Supplementary material
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC no. 130870 for 1, 130869 for 7 and
130868 for 37. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Acknowledgements
[3] (a) W.J. Evans, J.H. Meadows, W.E. Hunter, J.L. Atwood,
Organometallics 2 (1983) 1252. (b) M.D. Curtis, J. Real, J.
Am. Chem. Soc. 108 (1986) 4668. (c) S.M. Beshouri, P.E. Fan-
wick, I.P. Rothwell, J.C. Huffman, Organometallics 6 (1987)
891. (d) E. Carmona, J.M. Mar´ın, P. Palma, M.L. Poveda, J.
We are grateful to DGICYT (Project PB 97-0761)
and to Universidad de Alcala´ (Project E009/98) for
financial support of this research.

A. Castro et al. / Journal of Organometallic Chemistry 595 (2000) 36–53
53
Organomet. Chem. 377 (1989) 157. (e) A.C. Filippou, E.O.
Fischer, W. Gru¨nleitner, J. Organomet. Chem. 386 (1990) 333.
(f) A.C. Filippou, W. Gru¨nleitner, J. Organomet. Chem. 398
(1990) 99. (g) M.D. Curtis, J. Real, W. Hirpo, W.M. Butler,
Organometallics 9 (1990) 66. (h) A.C. Filippou, W. Gru¨nleitner,
E.O. Fischer, W. Imhof, G. Huttner, J. Organomet. Chem. 413
(1991) 165. (i) A.C. Filippou, W. Gru¨nleitner, C. Vo¨lkl, P.
Kiprof, J. Organomet. Chem. 413 (1991) 181. (j) A.C. Filippou,
C. Vo¨lkl, P. Kiprof, J. Organomet. Chem. 415 (1991) 375. (k) A.
Martin, M. Mena, M.A. Pellinghelli, P. Royo, R. Serrano, A.
Tiripicchio, J. Chem. Soc. Dalton Trans. (1993) 2117.
[16] (a) G.W.A. Fowles, D.A. Rice, D. Wilkins, J. Chem. Soc.
Dalton Trans. (1972) 2313; (1974) 1080. (b) R.R. Schrock, P.
Meakin, J. Am. Chem. Soc. 96 (1974) 5288. (c) S. Santini-Scam-
pucci, J.D. Riess, J. Am. Chem. Soc. Dalton Trans. (1973) 2436.
[17] (a) K. Nakamoto, in: M. Tsutsui (Ed.), Characterization of
Organometallics Compounds, Interscience, New York, 1969. (b)
R.J.H. Clark, M.A. Coles, J. Chem. Soc. Dalton Trans. (1974)
1462. (c) A. Antin˜olo, M. Fajardo, A. Otero, P. Royo, J.
Organomet. Chem. 234 (1982) 309; 246 (1983) 269; 265 (1984)
35.
[18] M.H. Chisholm, C.E. Hammond, D. Ho, J.C. Huffman, J. Am.
Chem. Soc. 108 (1986) 7860.
[19] (a) G.R. Newkome, W.E. Puckett, V.K. Gupta, G.E. Kiefer,
Chem. Rev. 86 (1986) 451 and references therein. (b) I. de
Castro, M.V. Galakhov, M. Go´mez, P. Go´mez-Sal, P. Royo,
Organometallics 15 (1996) 1362.
[4] (a) M.V. Galakhov, M. Go´mez, G. Jime´nez, M.A. Pellinghelli,
P. Royo, A. Tiripicchio, Organometallics 13 (1994) 1564. (b)
M.V. Galakhov, M. Go´mez, G. Jime´nez, P. Royo, M.A.
Pellinghelli, A. Tiripicchio, Organometallics 14 (1995) 1901. (c)
M.V. Galakhov, M. Go´mez, G. Jime´nez, P. Royo, M.A.
Pellinghelli, A. Tiripicchio, Organometallics 14 (1995) 2843. (d)
A. Castro, M.V. Galakhov, M. Go´mez, P. Go´mez-Sal, A. Mar-
t´ın, P. Royo, J. Organomet. Chem. 554 (1998) 185. (e) A. Castro,
M.V. Galakhov, M. Go´mez, F. Sa´nchez, J. Organomet. Chem.
580 (1999) 161.
[20] (a) A. Antin˜olo, J.M. de Ilarduya, A. Otero, P. Royo, A.M.M.
Lanfredi, A. Tiripicchio, J. Chem. Soc. Dalton Trans. (1988)
2685. (b) A. Antin˜olo, P. Espinosa, M. Fajardo, P. Go´mez-Sal,
C. Lo´pez-Mardomingo, A. Mart´ın-Alonso, A. Otero, J. Chem.
Soc. Dalton Trans. (1995) 1007. (c) A. Antin˜olo, A. Otero, M.
Fajardo, R. Gil-Sanz, M.J. Herra´nz, C. Lo´pez-Mardomingo, A.
Mart´ın, P. Go´mez Sal, J. Organomet. Chem. 533 (1997) 87. (d)
A. Antin˜olo, A. Otero, M. Fajardo, C. Garc´ıa-Yebra, C. Lo´pez-
Mardomingo, A. Mart´ın, P. Go´mez Sal, Organometallics 16
(1997) 2601. (e) A. Antin˜olo, F. Carrillo-Hermosilla, A. Otero,
M. Fajardo, A. Garce´s, P. Go´mez-Sal, C. Lo´pez-Mardomingo,
A. Mart´ın, C. Miranda, J. Chem. Soc. Dalton Trans. (1998) 59.
[21] R. Fandos, M. Go´mez, P. Royo, S. Garc´ıa-Blanco, S. Martinez-
Carrera, J. Sanz-Aparicio, Organometallics 6 (1987) 1581.
[5] M. Go´mez, P. Go´mez-Sal, G. Jimenez, A. Mart´ın, P. Royo, J.
Sa´nchez-Nieves, Organometallics 15 (1996) 3579.
[6] (a) K.B. Sharpless, R.C. Michaelson, J. Am. Chem. Soc. 95
(1973) 6136. (b) K.B. Sharpless, S. Tanaka, H. Yamamoto, H.
Nozaki, R.C. Mioh, J.D. Cutting, J. Am. Chem. Soc. 96 (1974)
5254. (c) K.B. Sharpless, T.R. Verhoeven, Aldrichimica Acta 12
(1979) 63. (d) K. Suzuki, E. Katayama, G. Tsuchihashi, Tetrahe-
dron Lett. 24 (1983) 4997. (e) B. Rickborn, in: B.M. Trock, I.
Fleming (Eds.), Comprehensive Organic Synthesis, vol. 3, Perga-
mon Press, New York, 1991, pp. 721–732. (f) C.M. Marson,
A.J. Walker, J. Pickering, A.D. Hobson, R. Wrigglesworth, S.J.
Edge, J. Org. Chem. 58 (1993) 5994.
2
2
,
[22] C(sp )ꢀN(sp ) 1.28 A in imines; J. March, Advanced Organic
Chemistry. Reactions, Mechanism and Structure, Wiley, New
York, 1985, p. 19.
[7] (a) L. Kloppenburg, J.L. Petersen, Organometallics 16 (1997)
3548. (b) M.A. Putzer, B. Neumu¨ller, K. Dehnicke, Z. Anorg.
Allg. Chem. 624 (1998) 57
[8] R.P. Planalp, R.A. Andersen, Organometallics 2 (1983) 1675.
[9] R.L. Huff, S.-Y. Wang, K. Abboud, J.M. Boncella,
Organometallics 16 (1997) 1779.
[23] (a) J.A. McCleverty, G. Wilkinson, J. Chem. Soc. (1963) 4096.
(b) H.G. Alt, J. Organomet. Chem. 127 (1977) 349.
[24] J. Teuben, in: T.J. Marks, I.L. Fragala (Eds.), Fundamental and
Technological Aspects of Organo-f-Element Chemistry, Dor-
drecht, Holland, 1986.
[25] K. Tatsumi, A. Nakamura, P. Hofmann, P. Stauffert, R. Hoff-
mann, J. Am. Chem. Soc. 107 (1985) 4440.
[26] (a) G. Fachinetti, C. Floriani, J. Organomet. Chem. 71 (1974)
C5. (b) G. Fachinetti, G. Fochi, C. Floriani, J. Chem. Soc.
Dalton Trans. (1977) 1946. (c) K.G. Moloy, T.J. Marks, J. Am.
Chem. Soc. 106 (1984) 7051.
[10] P. Zanella, N. Brianese, U. Castellato, F. Ossala, M. Porchin, G.
Rossetto, R. Graziani, J. Chem. Soc. Dalton Trans. (1987) 2039.
[11] R.B. King, M.B. Bisnette, J. Organomet. Chem. 8 (1967) 287.
[12] (a) E.R. Lippincott, R.D. Nelson, Spectrochim. Acta 10 (1958)
307. (b) H.P. Fritz, Adv. Organomet. Chem. 1 (1964) 269. (c)
F.A. Cotton, T.J. Marks, J. Am. Chem. Soc. 91 (1969) 7281. (d)
A. Castro, M. Go´mez, P. Go´mez-Sal, A. Manzanero, P. Royo, J.
Organomet. Chem. 518 (1996) 37.
[13] (a) D.F. Ball, P.L. Goggin, D.G. McKean, L.A. Woodward,
Spectrochim. Acta 16 (1960) 1358. (b) M. Go´mez, G. Jimenez, P.
Royo, J.M. Selas, P.R. Raithby, J. Organomet. Chem. 439
(1992) 147. (c) I. de Castro, J. de la Mata, M. Go´mez, P.
Go´mez-Sal, P. Royo, J.M. Selas, Polyhedron 11 (1992) 1023.
[14] (a) F. Bolhius, E.J.M. DeBoer, J.H. Teuben, J. Organomet.
Chem. 170 (1979) 299. (b) E. Klei, J.H. Telgen, J.H. Teuben, J.
Organomet. Chem. 209 (1981) 297. (c) L.R. Chamberlain, L.D.
Durfee, P.E. Fanwick, L. Kobriger, S.L. Latesky, A.K. McMul-
len, I.P. Rothwell, K. Folting, J.C. Huffman, W.E. Streib, R.
Wang, J. Am. Chem. Soc. 109 (1987) 390.
[27] P.J. Fagan, J.M. Manriquez, S.H. Vollmer, S.C. Day, V.W. Day,
T.J. Marks, J. Am. Chem. Soc. 103 (1981) 2206.
[28] (a) G. Paolucci, G. Rossetto, P. Zanella, K. Yunlu, R.O. Fis-
cher, J. Organomet. Chem. 272 (1984) 363. (b) A Dormond, A.
Aaliti, C. Moise, J. Chem. Soc. Chem. Commun. (1985) 1231. (c)
M.H. Chisholm, C.E. Hammond, J.C. Huffman, Organometal-
lics 6 (1987) 210. (d) D.M. Roddick, B.D. Santarsiero, J.E.
Bercaw, J. Am. Chem. Soc. 107 (1985) 4670.
[29] (a) C.D. Wood, R.R. Schrock, J. Am. Chem. Soc. 101 (1979)
5421. (b) M.D. Curtis, S. Thanedar, W.M. Butler, Organometal-
lics 3 (1984) 1855. (c) T.Y. Meyer, L.R. Garner, N.C. Baen-
zinger, L.W. Messerle, Inorg. Chem. 29 (1990) 4045.
[30] (a) W.A. Nugent, J.M. Mayer, Metal–Ligand Multiple Bonds,
Wiley, New York, 1988. (b) G. Parkin, A. Van Asselt, D.J.
Leahy, L.-R. Whinnery, N.G. Hua, R.W. Quan, L.M. Henling,
W.P. Schaefer, B.D. Santarsiero, J.E. Bercaw, Inorg. Chem. 31
(1992) 82.
[15] (a) D.C. Bradley, M.B. Hursthouse, A.J. Howes, A.N. de M.
Jelfs, J.D. Runnacles, M. Thornton-Pett, J. Chem. Soc. Dalton
Trans. (1991) 841. (b) D.N. Williams, J.P. Mitchell, A.D. Poole,
U. Siemeling, W. Clegg, D.C.R. Hockless, P.A. O’Neil, V.C.
Gibson, J. Chem. Soc. Dalton Trans. (1992) 739.
[31] G.M. Sheldrick, SHELX-97. Programs for Crystal Structure Anal-
ysis (Release 97-2), University of Go¨ttingen, Germany, 1997.