Ligand-induced and reductively induced alkyne-isocyanide coupling reactions of Mo(CnBut)3(PhC≡CPh)(η5-C5M e55)][BF4]

Article abstract of DOI:10.1021/om020313y

The complex [Mo(CO)(PhC=CPh)₂(η⁵-C₅Me₅)] [BF₄] reacts with 3 equiv of CNBu^t to yield the mixed alkyne - isocyanide complex [Mo(CNBu^t)₃(PhC≡CPh)(??⁵-C₅ Me₅)][BF₄], 1. Reaction of 1 with a fourth equivalent of CNBu^t generates [Mo{=C(NHBu^t)C(Ph)=C(Ph)CN}(CNBu^t)₂(η⁵ -C₅Me₅)] [BF₄], 2, containing an η³-vinylcarbene ligand formed from the coupling of two of the coordinated isocyanide ligands with the diphenylacetylene, with concomitant protonation of one of these isocyanide fragments and dealkylation of the other. Complex 2 may be deprotonated to give [Mo{C(=NBu^t)C(Ph)=C(Ph)CN}(CNBu^t)₂(η⁵ -C₅Me₅)], 3. Protonation of 1 with HBF₄·Et₅O generates [Mo{=C(Ph)C(Ph)C=NHBu^t}(CNBu^t)₂(η⁵ C₅Me₅)][BF₄]₂, 4, by inducing the coupling of a protonated isocyanide ligand with diphenylacetylene, and 4 reacts with CNBu^t to give 2. A similar reaction of 4 with P(OMe)₃ generates [Mo{=C(NHBu^t)C(Ph)=C(Ph)CN}(CNBu^t){P(OMe)₃}( η⁵-C₅Me₅)][BF₄], 5, involving the same coupling and elimination pattern. The diphenylacetylene and CNBu^t ligands of 1 may also be reductively coupled. Thus, treatment of 1 with sodium-mercury amalgam and subsequent protonation with HBF₄-Et₂O gives the metallacyclopentatriene-like [Mo{=C(NHBu^t)C(Ph)=C(Ph)C(NHBu^t)}(CNBu^t)(η ⁵-C₅Me₅)][BF₄], 6, or [Mo{=C(NHBu^t)C(Ph)C(Ph)CH-NHBu^t}(CNBu^t)(η ⁵C₅Me₅)][BF₄], 7, depending upon the solvent. Complex 7 contains an N-protonated η⁴monoazadiene ligand with a pendant carbene functionality that is also coordinated to the metal. The crystal structures of 1, 2, 3, 6, and 7 have been determined.

Full text of DOI:10.1021/om020313y

3454
Organometallics 2002, 21, 3454-3463
Liga n d -In d u ced a n d Red u ctively In d u ced
Alk yn e-Isocya n id e Cou p lin g Rea ction s of
[Mo(CNBu t)3(P h CtCP h )(η5-C5Me5)][BF 4]
Christopher J . Adams, Kirsty M. Anderson, Ian M. Bartlett, Neil G. Connelly,*
A. Guy Orpen, and Timothy J . Paget
School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K.
Received April 19, 2002
The complex [Mo(CO)(PhCtCPh)2(η5-C5Me5)][BF4] reacts with 3 equiv of CNBut to yield
the mixed alkyne-isocyanide complex [Mo(CNBut)3(PhCtCPh)(η5-C5Me5)][BF4], 1. Reaction
of 1 with a fourth equivalent of CNBut generates [Mo{dC(NHBut)C(Ph)dC(Ph)CN}(CNBut)2-
(η5-C5Me5)][BF4], 2, containing an η3-vinylcarbene ligand formed from the coupling of two of
the coordinated isocyanide ligands with the diphenylacetylene, with concomitant protonation
of one of these isocyanide fragments and dealkylation of the other. Complex 2 may be
deprotonated to give [Mo{C(dNBut)C(Ph)dC(Ph)CN}(CNBut)2(η5-C5Me5)], 3. Protonation of
1 with HBF4‚Et2O generates [Mo{dC(Ph)C(Ph)CdNHBut}(CNBut)2(η5-C5Me5)][BF4]2, 4, by
inducing the coupling of a protonated isocyanide ligand with diphenylacetylene, and 4 reacts
with CNBut to give 2. A similar reaction of 4 with P(OMe)3 generates [Mo{dC(NHBut)C-
(Ph)dC(Ph)CN}(CNBut){P(OMe)3}(η5-C5Me5)][BF4], 5, involving the same coupling and
elimination pattern. The diphenylacetylene and CNBut ligands of 1 may also be reductively
coupled. Thus, treatment of 1 with sodium-mercury amalgam and subsequent protonation
with HBF4‚Et2O gives the metallacyclopentatriene-like [Mo{dC(NHBut)C(Ph)dC(Ph)C-
(NHBut)}(CNBut)(η5-C5Me5)][BF4], 6, or [Mo{dC(NHBut)C(Ph)C(Ph)CH-NHBut}(CNBut)(η5-
C5Me5)][BF4], 7, depending upon the solvent. Complex 7 contains an N-protonated η4-
monoazadiene ligand with a pendant carbene functionality that is also coordinated to the
metal. The crystal structures of 1, 2, 3, 6, and 7 have been determined.
In tr od u ction
Me5)][BF4]2 reacts readily with 3 equiv of CNBut to
produce the mixed alkyne-isocyanide complex [Mo-
(CNBut)3(PhCtCPh)(η5-C5Me5)][BF4], 1, which may be
isolated in good yield as an orange crystalline solid.
(Microanalytical and IR data for all compounds are
given in Table 1.) By contrast, the CNxyl analogue could
not be prepared as a solid,1 but the cyclopentadienyl
analogue is known.3 Compound 1 shows the expected
three ν(CN) bands in the IR spectrum (2163m sh, 2139s,
and 2120m sh cm-1) and has two peaks in the 13C NMR
spectrum, at 62.5 and 72.8 ppm, typical of a coordinated
alkyne acting as a two-electron donor.4 The room-
We have recently reported the results of our investi-
gations of the reactivity of mixed CNxyl-diphenylacet-
ylene (CNxyl ) 2,6-dimethylphenylisocyanide) com-
pounds of molybdenum.1 Our initial intention was to
examine redox-induced reactions between these two
coordinated ligands, but instead we found that they are
readily thermally coupled. This paper describes a paral-
lel investigation of similar systems with tert-butyliso-
cyanide, CNBut, and reports substantially different
results. Thus, [Mo(CNBut)3(PhCtCPh)(η5-C5Me5)][BF4],
1, formed from the reaction between CNBut and [Mo-
(CO)(PhCtCPh)2(η5-C5Me5)][BF4], does undergo reac-
tion with further CNBut to give products containing
thermally coupled ligands, but these are of different
structural types from those previously reported. Com-
pound 1 can also be reduced, yielding metallacyclic
systems formed by coupling isocyanide and alkyne
ligands.
1
temperature H NMR spectrum (Table 2) shows broad
peaks for the tert-butyl groups of the isocyanide ligands,
probably because of a fluxional process involving rota-
tion of the Mo(CNBut)3 tripod, similar to that observed
in [Mo(CO)(CNR)3(η5-C5Me5)]+.5 At -40 °C these signals
are resolved into two sharp signals in a 2:1 ratio.
Allowing a thf-n-hexane solution of the compound to
evaporate gave crystals of 1 suitable for X-ray diffrac-
tion; the crystal structure of the cation of 1 is shown in
Figure 1, and selected bond lengths and angles are given
in Table 3. The compound is based upon a square
Resu lts
Syn th esis of [Mo(CNBu t)3(P h CtCP h )(η5-C5Me5)]-
[BF 4]. A CH2Cl2 solution of [Mo(CO)(PhCtCPh)2(η5-C5-
(2) Leoni, P.; Marchetti, F.; Pasquale, M.; Zanello, P. J . Chem. Soc.,
Dalton Trans. 1988, 635.
* Corresponding author. Tel: +44 117 9288162. Fax: +44 117
9290509. E-mail: Neil.Connelly@bristol.ac.uk.
(1) Adams, C. J .; Anderson, K. M.; Bartlett, I. M.; Connelly, N. G.;
Orpen, A. G.; Paget, T. J .; Phetmung, H.; Smith, D. W. J . Chem. Soc.,
Dalton Trans. 2001, 1284.
(3) Davidson, J . L.; Green, M.; Nyathi, J . Z.; Stone, F. G. A.; Welch,
A. J . J . Chem. Soc., Dalton Trans. 1977, 2246
(4) Templeton, J . L.; Ward, B. C. J . Am. Chem. Soc. 1980, 102, 3288.
(5) Lawless, G.; McNally, G.; Manning, A. R.; Cunningham D.;
McArdle, P. Polyhedron 1986, 5, 1741.
10.1021/om020313y CCC: $22.00 © 2002 American Chemical Society
Publication on Web 06/29/2002

Alkyne-Isocyanide Coupling Reactions
Ta ble 1. Micr oa n a lytica l a n d IR Da ta for Com p ou n d s 1-7
IR
ν(CNBut)/cm-1 b
Organometallics, Vol. 21, No. 16, 2002 3455
microanalysis (%)a
H
compound
C
N
[Mo(CNBut)3(PhCtCPh)(η5-C5Me5)][BF4], 1
2165w, 2140, 2123m
2192wc
62.7 (62.8)
61.9 (62.2)
7.2 (7.0)
7.0 (6.9)
5.5 (5.6)
7.2 (7.2)
[Mo{dC(NHBut)C(Ph)dC(Ph)CN}(CNBut)2(η5-C5Me5)][BF4], 2
2147, 2123
[Mo{C(dNBut)C(Ph)dC(Ph)CN}(CNBut)2(η5-C5Me5)], 3
2180wc
69.9 (70.2)
7.6 (7.7)
8.1 (8.2)
2107, 2056m
2185, 2171 sh
2192wc
2135
2122
[Mo{dC(Ph)C(Ph)dCdNHBut}(CNBut)2(η5-C5Me5)][BF4]2, 4
56.4 (56.2)
55.7 (56.1)
6.6 (6.4)
6.4 (6.6)
4.9 (5.0)
5.0 (5.2)
[Mo{dC(NHBut)C(Ph)dC(Ph)CN}(CNBut){P(OMe)3}(η5-C5Me5)][BF4], 5
[Mo{dC(NHBut)C(Ph)dC(Ph)C(NHBut)}(CNBut)(η5-C5Me5)][BF4], 6
[Mo{dC(NHBut)C(Ph)C(Ph)CHNHBut}(CNBut)(η5-C5Me5)][BF4]2, 7
62.7 (62.7)
56.1 (56.2)
7.6 (7.3)
6.6 (6.4)
5.4 (5.6)
5.0 (5.0)
2176
a
b
Calculated values in parentheses. In CH2Cl2. c Terminal CN.
Ta ble 2. NMR Sp ectr oscop ic Da ta (δ, J /Hz) for Com p ou n d s 1-7 (a ll sp ectr a r ecor d ed a t r oom tem p er a tu r e
in CD2Cl2 u n less oth er w ise sta ted )
compound
1H (δ/ppm)
13C (δ/ppm)
[Mo(CNBut)3(PhCtCPh) (η5-C5Me5)]-
[BF4], 1a
1.34 (s, 18H, But), 1.55 (s, 9H, But), 1.84
(s, 15H, C5Me5), 6.97-7.40 (m, 10H, Ph)
11.7 (C5Me5), 30.7, 31.1 (CMe3), 57.7, 58.5
(CMe3), 62.5, 72.8 (CPh), 103.6 (C5Me5),
125.7, 126.1, 126.7, 128.5, 128.8, 128.9,
129.4, 131.8, 136.6, 139.6 (Ph), 156.1,
169.1 (CN)
9.7 (C5Me5), 29.3, 30.4, 31.1 (CMe3), 58.8,
59.9, 62.9 (CMe3), 68.1, 73.6 (CPh),
103.6 (C5Me5), 125.2 (Ph), 126.5 (CtN),
127.2, 127.4, 128.6, 128.8, 131.9, 137.9,
139.4 (Ph), 162.6, 167.7 (CN), 244.5
(ModC)
8.9 (C5Me5), 30.9, 31.0, 31.6 (CMe3), 34.26
(CPh), 56.9, 57.6, 60.9 (CMe3), 63.9
(CPh), 99.8 (C5Me5), 122.8, 125.1, 126.5,
127.3, 127.3 (Ph), 128.9 (CtN), 131.6,
143.0, 144.5 (Ph), 180.9, 187.9 (CN),
205.7 (ModC)
[Mo{dC(N(H)But)C(Ph)dC(Ph)CN}-
(CNBut)2(η5-C5Me5)][BF4], 2
1.17 (s, 9H, But), 1.24 (s, 9H, But), 1.71
(s, 9H, But), 1.88 (s, 15H, C5Me5),
6.92-7.35 (m, 10H, Ph)
[Mo{C(dNBut)C(Ph)dC(Ph)CN}(CNBut)2- 0.98 (s, 9H, But), 1.20 (s, 9H, But), 1.56
(η5-C5Me5)], 3
(s, 9H, But), 1.77 (s, 15H, C5Me5),
6.81-7.37 (m, 10H, Ph)
[Mo{dC(Ph)C(Ph)dCdNHBut}(CNBut)2-
(η5-C5Me5)][BF4]2, 4
1.20, 1.62, 1.65 (each s, 9H, But), 2.04
(s, 15 H, C5Me5), 7.03-7.08 (m, 2H, Ph),
7.30-7.35 (m, 3H, Ph), 7.75-7.97 (m,
5H, Ph), 10.41 (br s, 1H, NH)
11.0 (C5Me5), 28.1, 29.7, 29.8 (CMe3), 60.7,
61.3, 61.4, 66.7 (3 × CMe3 and 1 ×
C(Ph)dCdN), 109.8 (C5Me5), 127.1,
129.5, 130.3, 130.7, 132.5, 137.7, 138.1
(Ph), 205.5 (CdN), 288.4 (MdC)
10.4 (C5Me5), 29.6, 29.9 (CMe3), 55.2 (d,
2J CP ) 9.8 Hz, OCH3), 58.9, 64.2 (CMe3),
[Mo{dC(NHBut)C(Ph)C(Ph)CN}(CNBut)-
{P(OMe)3}(η5-C5Me5)][BF4], 5b
1.15, 1.18 (each s, 9 H, But), 1.86 (s, 15
3
H, C5Me5), 3.82 (d, 9H, J (HP) ) 10.6 Hz,
2
OMe), 7.05-7.45 (m, 10H, Ph)
73.7 (d, J CP ) 4.9 Hz, CPh), 104.4
(C5Me5), 125.6, 127.4, 127.6, 128.0, 128.3,
128.4, 132.1, 136.3, 140.7 (Ph and CtN),
2
249.2 (d, J CP ) 15.7 Hz, MdC)
[Mo{dC(NHBut)C(Ph)dC(Ph)C(NHBut)}- 1.27, 1.30, 1.43 (each s, 9 H, But), 1.69
8.9 (C5Me5), 30.2, 30.3, 30.7 (CMe3), 48.6,
49.3 (CPh), 57.4, 58.6, 63.1 (CMe3),
104.6 (C5Me5), 125.0, 125.0, 125.5, 126.9,
128.0, 128.2, 129.3, 140.7, 143.2 (Ph),
165.2 (CNBut), 234.0, 248.7 (MdC)
11.0 (C5Me5), 28.8, 30.2, 30.3 (CMe3), 61.4,
62.6, 63.8 (CMe3), 68.6, 85.2, 95.4 (M-C),
111.8 (C5Me5), 127.6, 128.2, 129.9, 130.1,
130.6, 130.7, 130.8, 131.1, 131.7, 132.2
(Ph), 234.4 (MdC)
(CNBut)(η5-C5Me5)][BF4], 6
(s, 15 H, C5Me5), 7.02-7.48 (m, 10H, Ph)
7.53 (s, 1H, NH) 9.04 (br s, 1H, NH)
[Mo{dC(NHBut)C(Ph)C(Ph)CHNHBut}-
(CNBut)(η5-C5Me5)][BF4]2, 7
1.17, 1.45, 1.69 (each s, 9 H, But), 1.85
3
(s, 15 H, C5Me5), 3.05 (d, 1H, J (HH)
8.8 Hz, CH), 7.10-7.15 (m, 2H, Ph),
7.32-7.57 (m, 9H, Ph and NH), 9.42
(br s, 1H, NH)
a
b
Recorded at -40 °C. Also shows δ (31P) ) 162.0 ppm.
C5H5)2], the only previously crystallographically char-
acterized molybdenum compound containing diphenyl-
acetylene acting as a two-electron donor.6
pyramid with the centroid of the C5Me5 ligand forming
the apex, and the three terminal carbon atoms of the
isocyanides basal vertices; the angle C(21)-C(11)-
C(16) between these three atoms is 93°. The molybde-
num atom lies 0.53 Å above the plane formed by these
three atoms, which is at an angle of 7.2° to the
cyclopentadienyl ring. The carbon atom C(27) of the
diphenylacetylene ligand lies approximately 1 Å below
the fourth corner of the square base. The Mo-Cisocyanide
distances are in the range previously reported for Mo-
CNBut compounds,5 although at 2.06 Å the bond Mo-
(1)-C(11) trans to the alkyne is shorter than the other
two (2.12, 2.14 Å). The CtC distance of 1.27 Å is
virtually the same as that seen in [Mo(PhCtCPh)(η5-
F or m a tion of Meta lla cycles. Reaction of 1 with a
further equivalent of CNBut, or of [Mo(CO)(PhCtCPh)2-
(η5-C5Me5)][BF4] with 4 equiv of CNBut, produces [Mo-
{dC(NHBut )C(Ph)dC(Ph)CN}(CNBut )2(η5-C5Me5)]-
[BF4], 2 (Scheme 1), containing an η3(4e)-vinylcarbene;
overall, the reaction involves coordination of a fourth
isocyanide molecule, insertion of the diphenylacetylene
into two of the metal-isocyanide bonds, the gain of one
proton, and the loss of [But]+. Formation of 2 is slow,
(6) (a) De Cian, A.; Colin, J .; Schappacher, M.; Ricard, L.; Weiss, R.
J . Am. Chem. Soc. 1981, 103, 1850.

3456 Organometallics, Vol. 21, No. 16, 2002
Adams et al.
Sch em e 1a
a
R ) But.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p ou n d 1
Mo(1)-C(11)
Mo(1)-C(21)
Mo(1)-C(16)
Mo(1)-C(27)
Mo(1)-C(26)
2.061(4)
2.115(4)
2.139(4)
2.174(4)
2.206(3)
C(11)-N(1)
C(16)-N(2)
C(21)-N(3)
C(26)-C(27)
1.152(4)
1.154(5)
1.155(4)
1.267(5)
C(11)-Mo(1)-C(21) 81.60(14) C(27)-Mo(1)-C(26) 33.62(13)
C(11)-Mo(1)-C(16) 88.89(14) N(1)-C(11)-Mo(1) 174.5(3)
C(21)-Mo(1)-C(16) 150.57(14) C(11)-N(1)-C(12) 168.1(4)
C(11)-Mo(1)-C(27) 119.31(13) N(2)-C(16)-Mo(1) 173.9(3)
C(21)-Mo(1)-C(27) 80.00(13) C(16)-N(2)-C(17) 173.6(4)
C(16)-Mo(1)-C(27) 80.60(13) N(3)-C(21)-Mo(1) 172.7(3)
C(11)-Mo(1)-C(26) 85.73(13) C(21)-N(3)-C(22) 178.1(4)
C(21)-Mo(1)-C(26) 74.81(13) C(27)-C(26)-C(28) 146.3(4)
C(16)-Mo(1)-C(26) 76.77(13) C(26)-C(27)-C(34) 147.5(4)
deshielded carbenoid atom is at 244 ppm in the 13C
spectrum. There are nine 13C peaks observed between
125 and 140 ppm in this spectrum; eight are due to the
two phenyl rings and one to the cyanide group, but the
latter has not been specifically assigned.
F igu r e 1. Structure of the cation of 1. Hydrogen atoms
have been omitted for clarity.
Crystals suitable for X-ray analysis were grown by
allowing n-hexane to diffuse into a concentrated CH2Cl2
solution of 2; the cation of 2 is shown in Figure 2, and
Table 4 contains selected bond lengths and angles. The
carbon atoms C(17) and C(18) originating from the
diphenylacetylene are bonded to the metal by single
bonds (Mo-C distances of 2.27 and 2.32 Å, respectively);
the double bond between Mo(1) and C(29) is much
shorter (2.02 Å). The angles around this carbenoid atom
C(29) sum to 356.4°, showing that it is sp2 hybridized
with an appropriately planar coordination geometry.
The amine proton H(2A) was located in the refinement
and is situated such that N(2) and its two connected
atoms are coplanar with C(29) and the atoms bonded
to it. This allows some delocalization of the amine lone
pair into the metal-carbon antibonding orbital, creating
taking 3-4 days at room temperature, and protons are
presumably either adventitious or come from the rear-
rangement of the eliminated [But]+ moiety to (CH3)2Cd
CH2 and H+.7 However, upon adding HBF4 to a mixture
of 1 and CNBut, complete conversion to 2 is achieved
in about 30 s.
Complex 2 shows three bands in the ν(CN) region of
the IR spectrum. In CH2Cl2, the terminal cyanide
stretch gives a weak band at 2192 cm-1, and the two
isocyanides give strong absorptions at 2147 and 2123
cm-1. The N-H stretch gives a broad band at 3280 cm-1
in Nujol. The amino proton is apparent as a broad peak
1
at 7.98 ppm in the H NMR spectrum, and the strongly
(7) Smith, M. B.; March, J . Advanced Organic Chemistry, 5th ed.;
Wiley-Interscience: New York, 2001.

Alkyne-Isocyanide Coupling Reactions
Organometallics, Vol. 21, No. 16, 2002 3457
F igu r e 3. Structure of 3. Hydrogen atoms have been
omitted for clarity.
F igu r e 2. Structure of the cation of 2. Hydrogen atoms
[except H(2A)] have been omitted for clarity.
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p ou n d 3
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p ou n d 2
Mo(1)-C(11)
Mo(1)-C(16)
Mo(1)-C(36)
Mo(1)-C(29)
Mo(1)-C(22)
N(1)-C(11)
2.032(7)
2.078(7)
2.104(6)
2.238(6)
2.326(6)
1.161(8)
N(2)-C(16)
N(3)-C(21)
N(4)-C(36)
C(21)-C(22)
C(22)-C(29)
C(29)-C(36)
1.164(7)
1.137(8)
1.270(8)
1.460(9)
1.464(9)
1.473(9)
Mo(1)-C(29)
Mo(1)-C(39)
Mo(1)-C(40)
Mo(1)-C(17)
Mo(1)-C(18)
N(1)-C(40)
2.018(3)
2.058(4)
2.129(3)
2.267(3)
2.318(3)
1.146(4)
N(2)-C(29)
N(3)-C(39)
N(4)-C(41)
C(17)-C(29)
C(17)-C(18)
C(18)-C(41)
1.311(4)
1.150(4)
1.147(4)
1.436(4)
1.469(4)
1.445(5)
C(11)-Mo(1)-C(16)
C(11)-Mo(1)-C(36)
81.8(2) N(3)-C(21)-C(22)
175.4(7)
C(29)-Mo(1)-C(39) 84.20(12) C(18)-C(17)-Mo(1) 73.19(17)
C(29)-Mo(1)-C(40) 129.99(12) C(41)-C(18)-C(17) 113.8(3)
C(39)-Mo(1)-C(40) 81.24(12) C(41)-C(18)-Mo(1) 110.5(2)
C(29)-Mo(1)-C(17) 38.61(11) C(17)-C(18)-Mo(1) 69.46(17)
C(29)-Mo(1)-C(18) 65.76(11) N(2)-C(29)-C(17) 134.0(3)
C(39)-Mo(1)-C(18) 126.11(12) N(2)-C(29)-Mo(1) 144.3(2)
C(40)-Mo(1)-C(18) 85.47(11) C(17)-C(29)-Mo(1) 80.14(18)
C(17)-Mo(1)-C(18) 37.35(10) N(3)-C(39)-Mo(1) 178.2(3)
79.0(2) C(21)-C(22)-C(29) 113.1(5)
C(16)-Mo(1)-C(36) 124.6(2) C(21)-C(22)-Mo(1) 108.8(4)
C(36)-Mo(1)-C(29)
C(11)-Mo(1)-C(22) 127.9(2) C(22)-C(29)-C(36) 109.1(5)
C(16)-Mo(1)-C(22)
C(36)-Mo(1)-C(22)
C(29)-Mo(1)-C(22)
N(1)-C(11)-Mo(1)
N(2)-C(16)-Mo(1)
39.5(2) C(29)-C(22)-Mo(1)
68.0(3)
88.7(2) C(22)-C(29)-Mo(1)
65.2(2) C(36)-C(29)-Mo(1)
37.4(2) N(4)-C(36)-C(29)
178.1(5) N(4)-C(36)-Mo(1)
170.6(5) C(29)-C(36)-Mo(1)
74.6(3)
65.3(3)
143.5(6)
140.8(5)
75.2(3)
C(29)-C(17)-C(18) 109.2(3)
N(1)-C(40)-Mo(1) 170.7(3)
C(29)-C(17)-Mo(1) 61.26(16) N(4)-C(41)-C(18) 176.7(4)
formal change in bonding, but both are still within
double-bond range.
a substantial degree of carbon-nitrogen double-bond
To investigate the formation of 2 further, a solution
of 1 was reacted with HBF4 in the absence of additional
isocyanide. In thf, this results in the rapid precipitation
of a dark green compound 4, which is stable in the solid
state but decomposes (mainly to 2) if left in solution for
extended periods. For this reason crystals suitable for
X-ray diffraction have not been obtained, but on the
basis of the analytical data discussed below 4 is formu-
lated as [Mo{dC(Ph)C(Ph)dCdNHBut}(CNBut)2(η5-C5-
Me5)][BF4]2, an η3(4e)-iminiumvinylcarbene complex
(Scheme 1). The reaction is fully reversible; deprotona-
tion of 4 with NEt3 results in the rapid conversion of 4
back to 1.
character. Thus, the distance C(29)-N(2) is only 1.31
Å.
Complex 2 may be deprotonated with NaN(SiMe3)2
to generate the neutral compound [Mo{C(dNBut)C-
(Ph)dC(Ph)CN}(CNBut)2(η5-C5Me5)], 3, containing an
η3(3e)-monoazadienyl ligand (Scheme 1). This reaction
is reversible; treatment of 3 with HBF4 regenerates 2.
The IR spectrum of 3 has ν(CN) for the isocyanide
ligands at 2107 and 2056 cm-1, at lower wavenumbers
than in 2 because of the lack of a charge on the complex
and the concomitant increase in metal-to-isocyanide
back-donation. The terminal cyanide vibration is also
moved to lower energy (2180 cm-1). The NMR spectra
of 3 are very similar to those of 2, the only significant
The solution IR spectrum of 4 shows two strong ν(CN)
absorptions bands (2185s and 2170s sh cm-1), consistent
with a bis(isocyanide) structure, and a band at 1668
cm-1 attributable to ν(CdN). In Nujol, an additional
band at 3243 cm-1 is present due to the N-H stretch.
1H NMR spectroscopy indicates three different But
groups, as well as a single broad NH peak at 10.41 ppm.
The 13C NMR spectrum contains a resonance at 288
ppm, due to the MdC unit, and another at 205 ppm due
to the CdN moiety. Elemental analysis also agrees with
the above formulation.
1
difference in the H spectrum being the disappearance
of the NH peak and in the 13C spectrum the upfield shift
of the R-carbon atom of the ring from 245 ppm (as a
carbene) to 206 ppm (as an imine). The crystal structure
of 3 (Figure 3 and Table 5) is also very similar to that
of the cation of 2, especially in the metallacyclic unit.
For example, Mo(1) and the atoms C(36), C(29), N(4),
and C(37) of the monoazadienyl ligand are again almost
coplanar. At 2.10 Å the Mo(1)-C(36) distance is slightly
longer and the C(36)-N(4) distance slightly shorter
(1.27 Å) than their counterparts in 2, in accord with the
Addition of CNBut to a CH2Cl2 solution of 4 results
in instant formation of 2. Furthermore, addition of

3458 Organometallics, Vol. 21, No. 16, 2002
Adams et al.
Sch em e 2a
F igu r e 4. Structure of the cation of 6. Most hydrogen
atoms have been omitted for clarity.
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p ou n d 6
Mo(1)-C(16)
Mo(1)-C(35)
Mo(1)-C(28)
Mo(1)-C(21)
C(16)-N(2)
2.033(5)
2.076(5)
2.186(5)
2.246(5)
1.322(6)
C(16)-C(21)
C(21)-C(28)
C(28)-C(35)
C(28)-C(29)
C(35)-N(3)
1.426(6)
1.461(7)
1.449(7)
1.479(8)
1.313(6)
a
R ) But.
P(OMe)3 to a solution of 4 generates [Mo{dC(NHBut)C-
(Ph)dC(Ph)CN}(CNBut){P(OMe)3}(η5-C5Me5)][BF4], 5,
a vinylcarbene analogous to 2 but with a trimethyl
phosphite ligand instead of one of the isocyanides
(Scheme 1). The IR and NMR spectral parameters of 5
C(16)-Mo(1)-C(35) 103.2(2)
C(35)-Mo(1)-C(28) 39.7(2)
C(35)-C(28)-C(21) 106.1(5)
C(35)-C(28)-C(29) 126.9(5)
C(16)-Mo(1)-C(21) 38.52(18) C(21)-C(28)-C(29) 127.0(5)
C(28)-Mo(1)-C(21) 38.46(18) C(35)-C(28)-Mo(1) 66.1(3)
N(2)-C(16)-C(21)
133.7(5)
C(21)-C(28)-Mo(1) 73.0(3)
C(29)-C(28)-Mo(1) 126.4(4)
N(2)-C(16)-Mo(1) 145.4(4)
C(21)-C(16)-Mo(1) 78.8(3)
C(16)-C(21)-C(28) 113.3(4)
C(16)-C(21)-Mo(1) 62.6(3)
C(28)-C(21)-Mo(1) 68.5(3)
2
are similar to those of 2, except that J CP coupling is
N(3)-C(35)-C(28)
126.8(5)
observed in the 13C NMR spectrum in the signals due
to the metal-bound carbon atoms.
N(3)-C(35)-Mo(1) 157.4(5)
C(28)-C(35)-Mo(1) 74.3(3)
Red u ction of 1. The cyclic voltammogram of 1 shows
a fully reversible diffusion-controlled oxidation wave at
0.60 V, followed by an irreversible process at 1.05 V,
but attempts to isolate products from the chemical
oxidation of 1 have been unsuccessful. There is also an
ill-defined reduction wave at approximately -1.2 V.
To investigate the reductive coupling of the isocyanide
and alkyne ligands, a thf solution of 1 was treated with
sodium-mercury amalgam. Isolation of the product
gave red-orange crystals, which were identified by X-ray
diffraction as the metallacyclopentatriene-like complex
[Mo{dC(NHBut)C(Ph)dC(Ph)C(NHBut)}(CNBut)(η5-C5-
Me5)][BF4], 6 (Scheme 2). As the formula of 6 differs
from that of the starting material 1 only by the addition
of two hydrogen atoms, it appears that two-electron
reduction of 1 is followed by the addition of two protons
to give the observed product.
ized and joined to each other by a single bond, and this
is borne out by examination of the crystal structure
(Figure 4 and Table 6). At 1.46 Å, this bond, C(21)-
C(28), is in the same range as the two CR-Câ single
bonds, C(35)-C(28) and C(16)-C(21), while the metal-
CR bonds, Mo(1)-C(35) and Mo(1)-C(16), are undoubt-
edly double. The distances between the molybdenum
atom and C(28) and C(21) are, at approximately 2.2 Å,
in the range expected for Mo-C single bonds. Further-
more, the metallacyclic ring is puckered in order to bring
these two â-carbon atoms to a position where they are
able to bond to the metal. There is no doubt, therefore,
that all four carbon atoms of this ring are bonded to
the metal, to donate the six electrons that enable the
metal to achieve an 18-electron configuration.
A planned synthesis of 6 was attempted by reduction
of 1 with sodium-mercury amalgam and subsequent
addition of HBF4, and if the protonation is carried out
in diethyl ether this is successful. However, in thf this
procedure does not yield 6 but instead gives [Mo{dC-
(NHBut )C(Ph)C(Ph)CHNHBut }(CNBut )(η5-C5Me5)]-
[BF4], 7, formed (at least formally) by the two-electron
reduction of 1 followed by triprotonation (Scheme 2).
The structure of the cation of 7 (Figure 5) is compli-
cated, but it contains a planar fragment comprising
N(1)-C(11)-C(16)-C(23). The carbon-carbon and car-
bon-nitrogen bond lengths are between those expected
for single and double bonds (Table 7) and are consistent
The IR spectrum of 6 has a single ν(CN) band at 2126
cm-1, with ν(NH) apparent at 3346 and 3260 cm-1 in
Nujol. The H NMR spectrum shows three different But
1
resonances and NH signals at 7.53 and 9.04 ppm. The
13C spectrum shows the two R-carbon atoms of the
metallacyclic ring at 234 and 249 ppm, consistent with
their carbenoid character, with the two â-carbon atoms
of this ring at around 49 ppm. The contact carbon atom
of the remaining isocyanide is at 165 ppm, typical of a
coordinated isocyanide.
The relatively low chemical shift of the â-carbon
atoms suggests that they are best viewed as sp3 hybrid-

Alkyne-Isocyanide Coupling Reactions
Organometallics, Vol. 21, No. 16, 2002 3459
Sch em e 3. (a ) F or m a tion of 4 via a n Im in oca r ben e a n d (b) Its Sim ila r ity w ith th e Rea ction Rep or ted by
Geoffr oy in Ref 9 (tol ) p-C6H4Me)
Ta ble 7. Bon d Len gth s (Å) a n d An gles (d eg) for
Com p ou n d 7
Mo(1)-C(30)
Mo(1)-C(16)
Mo(1)-C(23)
Mo(1)-N(1)
Mo(1)-C(11)
N(1)-C(11)
2.042(5)
2.228(4)
2.239(5)
2.259(4)
2.263(4)
1.408(6)
N(1)-C(12)
N(2)-C(30)
N(2)-C(31)
C(11)-C(16)
C(16)-C(23)
C(23)-C(30)
1.508(6)
1.305(6)
1.504(6)
1.403(6)
1.475(6)
1.423(6)
C(30)-Mo(1)-C(23) 38.49(16) N(1)-C(11)-Mo(1)
71.7(3)
C(16)-Mo(1)-C(23) 38.57(15) C(11)-C(16)-C(23) 115.6(4)
C(30)-Mo(1)-N(1) 109.56(16) C(11)-C(16)-Mo(1) 73.1(3)
C(16)-Mo(1)-C(11) 36.39(16) C(23)-C(16)-Mo(1) 71.1(2)
N(1)-Mo(1)-C(11)
C(11)-N(1)-C(12)
C(11)-N(1)-Mo(1)
C(30)-N(2)-C(31)
C(16)-C(11)-N(1)
36.28(15) C(30)-C(23)-C(16) 111.5(4)
124.3(4)
72.0(2)
C(30)-C(23)-Mo(1) 63.2(2)
C(16)-C(23)-Mo(1) 70.3(2)
133.5(4)
116.6(4)
N(2)-C(30)-C(23)
135.0(4)
N(2)-C(30)-Mo(1) 144.6(4)
C(23)-C(30)-Mo(1) 78.3(3)
C(16)-C(11)-Mo(1) 70.5(3)
and 3.05 ppm. The latter, proton H(3), is split into a
doublet (3J HH ) 8.8 Hz) by coupling to the neighboring
amine proton. The 13C spectrum has one carbene signal
at 234 ppm and three signals in the range 65-96 ppm
from the carbon atoms of the monoazadiene.
F igu r e 5. Structure of the cation of 7. Most hydrogen
atoms have been omitted for clarity.
with the fragment bonding as an N-protonated η4-
monoazadiene. Attached to this unit by a single bond
is another carbon atom, C(30), joined to the molybde-
num atom by a double bond (of length 2.04 Å) and thus
carbenoid in nature. The azadiene unit donates four
electrons to the metal and the carbene two, making the
positively charged ligand an overall six-electron donor.
Two of the three added protons are attached to the
nitrogen atoms of the isocyanide fragments involved in
the ring, one of these nitrogen atoms now forming part
of the diene; the third proton is, unusually, bonded to
the carbon atom of one of these isocyanide moieties.
Other spectroscopic data are entirely consistent with
this structure. The IR spectrum shows one ν(CN) band,
at 2176 cm-1, significantly higher than in 6 because of
the extra positive charge on the metal. The 1H NMR
spectrum shows three distinct But environments and
signals for two of the three added protons (the signal of
the third is hidden by those of the phenyl rings) at 9.43
Discu ssion
P r oton a tion of 1 a n d th e Dea lk yla tion of Coor -
d in a ted Isocya n id e. The protonation of metal-iso-
cyanide compounds is well known to produce iminocar-
bene (alternatively, aminocarbyne) compounds through
electrophilic addition to the nitrogen atom,8 but pro-
tonation of a mixed alkyne-isocyanide complex such as
1 appears to be a new reaction. We therefore postulate
that protonation of 1 leads initially to an iminocarbene,
which then undergoes an intramolecular reaction with
diphenylacetylene to form the observed product 4. This
is similar to a reaction reported by Geoffroy and
co-workers, where a carbene (generated in situ) couples
with diphenylacetylene to produce a vinylcarbene
(Scheme 3).9
(8) Crociani, B. Reactions of Coordinated Isocyanides. In Reactions
of Coordinated Ligands, Vol. 1; Braterman, P. S., Ed.; Plenum Press:
New York, 1986.

3460 Organometallics, Vol. 21, No. 16, 2002
Adams et al.
Sch em e 4. (a ) In itia l Sta ges of th e Do1tz Rea ction a n d (b) th e F or m a tion of 4 a n d Its Equ ilibr iu m w ith a n
Isom er ic Meta lla cyclea
a
This metallacycle may be trapped by addition of a ligand L, which causes rearrangement to give the observed product 2 or 5.
It is also similar (Scheme 4) to one of the initial stages
of the Do¨tz reaction,10 a benzannulation that couples
chromium-coordinated unsaturated (aryl or vinyl) alkoxy-
carbene ligands with alkynes and CO. One of the
intermediates in the Do¨tz reaction is a vinylcarbene, an
analogue of the iminiumvinylcarbene 4, and it has been
proposed that the next step in the Do¨tz reaction is an
intramolecular insertion of carbon monoxide into the
metal-carbene bond to give an η4(4e)-vinylketene
(Scheme 4).11 We propose that the next step in the
reaction of 4 with CNBut to form 2 is an analogous
intramolecular insertion, that of CNBut into the MdC
bond, producing an η4(4e) metallacyclic intermediate
(Scheme 4).
Me5)][BF4], 5, containing the same vinylcarbene ligand
as 2. The same vinylcarbene ligand is also formed when
the two-electron donor cyclohexylisocyanide (CNCy) or
chloride ion is added to a solution of 4 (respectively
producing [Mo{dC(NHBut)C(Ph)dC(Ph)CN}(CNBut)-
(CNCy)(η5-C5Me5)][BF4] and [Mo{dC(NHBut)C(Ph)d
C(Ph)CN}(CNBut)Cl(η5-C5Me5)]). Therefore, it appears
that in solution an equilibrium exists between 4 and a
metallacyclic isomer that is trapped by addition of a two-
electron donor ligand, L (Scheme 4). The metallacyclic
species that is created is unstable toward loss of a tert-
butyl cation, and the resulting elimination of [But]+ and
subsequent rearrangement generate the observed vi-
nylcarbene products 2 (L ) CNBut) and 5 {L ) P(OMe)3}
(Scheme 4). We have recently reported the formation
of a similar unstable metallacycle (containing CNxyl
instead of CNBut).1
That this insertion reaction is intramolecular, rather
than involving free isocyanide in the reaction mixture,
is shown by the reaction of 4 with ligands other than
CNBut. Thus, reaction of 4 with P(OMe)3 produces [Mo-
{dC(NHBut)C(Ph)dC(Ph)CN}(CNBut){P(OMe3)}(η5-C5-
The elimination of the R group from a coordinated
alkylisocyanide has been reported before.12-14 In most
cases the isocyanide involved is CNBut,12,13 as in the
present example, and normally the elimination is ther-
mally induced;12 for example, heating [Ru(CNBut)6]-
[PF6]2 under reflux in n-propanol for 12 h produces
(9) Garrett, K. E.; Sheridan, J . B.; Porreau, D. B.; Feng, W. C.;
Geoffroy, G. L.; Staley, D. L.; Rheingold, A. L. J . Am. Chem. Soc. 1989,
111, 8383.
(10) Do¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23, 587.
(11) Do¨tz, K. H.; Tomuschat, P. Chem. Soc. Rev. 1999, 28, 187

Alkyne-Isocyanide Coupling Reactions
Organometallics, Vol. 21, No. 16, 2002 3461
F igu r e 6. Metallacyclic core of 6. One metallacyclopropene ring is formed by the atoms Mo(1)-C(35)-C(28) and the
other by Mo(1)-C(16)-C(21), and the angle between the planes of these two rings is 35°.
F igu r e 7. Metallacyclic core of 7. The atoms N(1), C(11), C(16), and C(23) form the monoazadiene ring.
[Ru(CNBut)5(CN)][PF6]. However, in none of these prior
reports has elimination been triggered by coordination
of another ligand to the metal, and in none has the
resulting cyano group not been directly coordinated to
the metal.
Str u ctu r es of 6 a n d 7. Complex 6 contains a
metallacyclopentatriene, with an η4(6e) ligand derived
F igu r e 8. Planar (a), envelope (b), and twist (c) conforma-
from the diphenylacetylene and two of the isocyanide
tions adopted by metallacyclopentatriene.
ligands. Several metallacyclopentatrienes have been
reported,15 although only one system contains a six-
cycle because the ring is folded. This π-bonding orbital
constitutes the HOMO of the ligand and is able to
π-donate two further electrons to the metal. An envelope
configuration is adopted by the metallacycle in order
electron donor ligand such as that in 6.16 In all previous
studies the organic part of the ring is planar, giving the
metallacycle either a planar or envelope configuration;
in every case, each of the two terminal carbon atoms of
that this is geometrically possible (Figure 8).
the ring donates two electrons to the metal. In the
The metallacycle in 6 is different from all previous
examples in that it adopts a twist configuration, with a
example of six-electron metal-to-ligand donation, the
π-bond between the two â-carbon atoms of the organic
nonplanar organic fragment. Delocalization of the π-sys-
system is not conjugated with the rest of the metalla-
(15) For metallacyclopentatriene complexes see: (a) Albers, M. O.;
(12) (a) Posznik, G.; Carroll, P. J .; Wayland, B. B. Organometallics
1993, 12, 3410. (b) Farr, J . P.; Abrams, M. J .; Costello, C. E.; Davison,
A.; Lippard, S. J .; J ones, A. G. Organometallics 1985, 4, 139. (c) Tetrick,
S. M.; Walton, R. A. Inorg. Chem. 1985, 24, 3363. (d) Gambarotta, S.;
Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1984, 23, 1739.
(e) Bell, A.; Walton, R. A. J . Organomet. Chem. 1984, 263, 359. (f) Bell,
A.; Lippard, S. J .; Roberts, M.; Walton, R. A. Organometallics 1983, 2,
1562. (g) Giandomenico, C.; Hanau, L. H.; Lippard, S. J . Organome-
tallics 1982, 1, 142.
(13) (a) J ones, W. D.; Kosar, W. P. Organometallics 1986, 5, 1823.
(b) Crociani, B.; Nicoline, M.; Richards, R. L. Inorg. Chim. Acta 1975,
12, 53.
(14) (a) Werner, H.; Ho¨rlin, G.; J ones, W. D. J . Organomet. Chem.
1998, 562, 45. (b) Evans W. J .; Drummond, D. K. Organometallics
1988, 7, 797. (c) Treichel, P. M.; Hess, R. W. J . Chem. Soc., Chem.
Commun. 1970, 1626.
deWaal, D. J . A.; Liles, D. C.; Robinson, D. J .; Singleton, E.; Wiege,
M. B. J . Chem. Soc., Chem. Commun. 1986, 1680. (b) Gemel, C.;
LaPense´e, A.; Mauthner, K.; Mereiter, K.; Schmid, R.; Kirchner, K.
Monatsh. Chem. 1997, 128, 1189. (c) Pu, L.; Hasegawa, T.; Parkin, S.;
Taube, H. J . Am. Chem. Soc. 1992, 114, 2712. (d) Hirpo, W.; Curtis,
M. D. J . Am. Chem. Soc. 1988, 110, 5218. (e) Hessen, B.; Meetsma,
A.; van Bolhuis, F.; Teuben, J . H.; Helgesson, G.; J agner, S. Organo-
metallics 1990, 9, 1925. (f) Ernst, C.; Walter, O.; Dinjus, E.; Arzberger,
S.; Go¨rls, H. J . Prakt. Chem. 1999, 341, 801. (g) Ru¨ba, E.; Mereiter,
K.; Schmid, R.; Kirchner K. J . Chem. Soc., Chem. Commun. 2001, 1996.
(h) Becker, E.; Ru¨ba, E.; Mereiter, K.; Schmid, R.; Kirchner K.
Organometallics 2001, 20, 3851. (i) Curtis, M. D.; Real, J .; Hirpo, W.;
Butler, W. M. Organometallics 1990, 9, 66.
(16) (a) Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem.
Soc. 1988, 110, 8235. (b) Kriley, C. E.; Kerschner, J . L.; Fanwick, P.
E.; Rothwell, I. P. Organometallics 1993, 12, 2051.

3462 Organometallics, Vol. 21, No. 16, 2002
Adams et al.
tem is therefore broken between the two â-carbon atoms
C(21) and C(28), rather than between the R- and
â-carbons as in the example discussed above. Thus,
although formally a metallacyclopentatriene, the ligand
may also be regarded as containing two metallacyclo-
propene fragments linked by a single bond, C(21)-C(28),
of length 1.46 Å, and with an angle of 35° between them
(Figure 6). On comparing these aminometallacyclopro-
pene rings with other crystallographically characterized
aminometallacyclopropenes,17 features such as the short
carbon-nitrogen bond length and the planarity of the
nitrogen atom, commonly associated with heteroatom-
substituted (Fischer-type) carbenes, become apparent.
Previous metallacyclopentatrienes are all alkyl or aryl
substituted at the R-carbon atoms (i.e., Schrock car-
benes).
Overall, the metallacycle within 7 differs from that
of 6 only by the addition of a proton to one of the
R-carbon atoms of the ring, and therefore one end of the
ligand is still a metallacyclopropene ring similar to those
in 6. However, as reported above, the rest of the ligand
has become a protonated η4-monoazadiene. The struc-
ture of a compound containing a similar fragment,
namely, [Mo(CO)2(PBu3)2(η4-PhNHdCHCHdCHPh)],18
has been reported, though this was synthesized from
an unprotonated η4-monoazadiene compound. Many
more structures containing unprotonated analogues19
show structural features also found in 7, including the
coplanarity not only of the four atoms of the diene but
also of the atoms attached to the carbon atoms C(11)
and C(16) of the ring (Figure 7).
an unusual ligand formed from a protonated η4-
monoazadiene bonded to an aminocarbene functionality.
Exp er im en ta l Section
The preparation, purification, and reactions of the complexes
described were carried out under an atmosphere of dry
dinitrogen using dried and deoxygenated solvents. All com-
plexes are stable for short periods in air in the solid state. NMR
spectra were recorded on a J EOL GX400 spectrometer with
SiMe4 as an internal standard. IR spectra were recorded on a
Perkin-Elmer 1600 series FTIR spectrometer. Electrochemical
studies were carried out as previously described.20 Under the
conditions employed, E°′ for the one-electron oxidation of
ferrocene, added as an internal calibrant, is 0.47 V. Micro-
analyses were carried out by the staff of the Microanalytical
Service of the School of Chemistry at the University of Bristol.
Syn th eses. [Mo(CO)(PhCtCPh)2(η5-C5Me5)][BF4]2 was pre-
pared by a modification of the published procedure. To a purple
solution of [MoMe(CO)3(η5-C5Me5)]21 (4.28 g, 12.9 mmol) and
diphenylacetylene (15 g, 84 mmol) in CH2Cl2 (60 cm3) was
added HBF4 (54% in Et2O, 1.8 cm3, 13.0 mmol), causing the
solution to effervesce and become brown. Diethyl ether (60 cm3)
was then added, and the solution stored at 4 °C for 4 days.
The resulting orange crystals were isolated by filtration and
washed with diethyl ether, to give 4.30 g (6.1 mmol, 47%) of
the desired product, suitable for synthetic use.
[Mo(CNBu t)3(P h CtCP h )(η5-C5Me5)][BF 4], 1. To an or-
ange solution of [Mo(CO)(PhCtCPh)2(η5-C5Me5)][BF4] (1.51 g,
2.14 mmol) in CH2Cl2 (15 cm3) was added CNBut (0.73 cm3,
6.42 mmol). The solution was stirred for 1 h, during which
time it turned deep red. Diethyl ether (80 cm3) was slowly
added to give an orange microcrystalline solid, which was
isolated by filtration, washed copiously with diethyl ether, and
dried in vacuo, yield 1.49 g (93%).
[Mo{dC(NHBu t)C(P h )dC(P h )CN}(CNBu t)2(η5-C5Me5)]-
[BF 4], 2. To a solution of [Mo(PhCtCPh)2(CO)(η5-C5Me5)]
(0.500 g, 0.71 mmol) in thf (90 cm3) was added CNBut (0.322
cm3, 2.84 mmol). This solution was heated under reflux for 16
h, cooled, filtered through Celite, and evaporated to dryness.
The residue was redissolved in CH2Cl2 (10 cm3), and the pale
orange product precipitated by slow addition of n-hexane (100
cm3), yield 0.409 g (75%). This solid is sufficiently pure for
further experimental work, but may be recrystallized by
storage of a CH2Cl2-n-hexane solution at 4 °C.
Con clu sion s
The current paper reports the synthesis of the mixed
alkyne-isocyanide compound 1, which readily under-
goes ligand-coupling reactions. We have shown before1
that a similar alkyne-isocyanide system will react with
further isocyanide to give ligand-coupled products, but
whereas this only involved rearrangement of the moi-
eties present, the current paper reports a much rarer
isocyanide dealkylation reaction. Some understanding
of this process has been gained through selectively
protonating 1 and then introducing the additional ligand
(which does not have to be an isocyanide); it appears
that this additional ligand drives the dealkylation by
trapping an unstable intermediate. Such a process is
unprecedented: dealkylation reactions of coordinated
isocyanides are normally thermally induced.
A second theme is the reductively induced coupling
of the alkyne and isocyanide. Reduction and protonation
of 1 causes the formation of an η4(6e)-metallacyclopen-
tatriene, 6; this is the second such system known and
the first metallacyclopentatriene to contain a nonplanar
ligand. Consideration of the X-ray crystal structure
suggests that it may be regarded as two linked Fischer-
carbene type metallacyclopropenes. Further protonation
of this metallacycle generates compound 7, containing
[Mo{C(dNBu t)C(P h )dC(P h )CN}(CNBu t)2(η5-C5Me5)], 3.
A 0.6 M solution of NaN(SiMe3)2 in toluene (0.9 cm3, 0.54
mmol) was added to a suspension of 2 (0.40 g, 0.52 mmol) in
thf (20 cm3) and stirred for 20 min at room temperature. The
slightly cloudy red solution was then evaporated to dryness
and extracted with diethyl ether (4 × 20 cm3). n-Hexane (100
cm3) was added to the combined extracts, and the volume of
the red solution reduced to about 50 cm3 in vacuo. Storage
overnight at -20 °C gave 3 as a red crystalline solid, yield
0.25 g (70%).
[Mo{dC(P h )C(P h )dCdNH Bu t }(CNBu t )2(η5-C5Me 5)]-
[BF 4]2, 4. To a rapidly stirred solution of 1 (0.137 g, 0.183
mmol) in thf (10 cm3) was added 4 drops of HBF4‚Et2O, causing
the bottle-green product to precipitate. Stirring was continued
for 1 min, and then the product was isolated by filtration,
washed with diethyl ether (2 × 5 cm3), and dried in vacuo,
yield 0.118 g (77%).
[Mo{dC(NHBu t)C(P h )C(P h )CN}(CNBu t){P (OMe)3}(η5-
C5Me5)][BF 4], 5. A solution of 4 (0.079 g, 0.094 mmol) and
P(OMe)3 (0.02 cm3, 0.188 mmol) in CH2Cl2 (5 cm3) was stirred
for 30 min, producing a green-to-orange color change. n-
(17) (a) Dossett, S. J .; Li, S.; Mullica, D. F.; Sappenfield, E. L.; Stone,
F. G. A. Organometallics 1994, 13, 822. (b) Adams, R. D.; Chen, G.;
Chen, L.; Yin, J . Organometallics 1993, 12, 2644.
(18) tom Dieck, H.; Stamp, L.; Diercks, R.; Mu¨ller, C. New J . Chem.
1985, 9, 289.
(19) Imhof, W.; Go¨bel, A.; Braga, D.; De Leonardis, P.; Tedesco, E.
Organometallics 1999, 18, 736.
(20) Brown, N. C.; Carpenter, G. B.; Connelly, N. G.; Crossley, J .
G.; Martin, A.; Orpen, A. G.; Rieger, A. L.; Rieger, P. H.; Worth, G. H.
J . Chem. Soc., Dalton Trans. 1996, 3977.
(21) King, R. B.; Bisnette, M. B. J . Organomet. Chem. 1967, 8, 287.

Alkyne-Isocyanide Coupling Reactions
Organometallics, Vol. 21, No. 16, 2002 3463
Ta ble 8. Cr ysta l Da ta for Com p ou n d s 1-3, 6, a n d 7
1
2
3
6‚CHCl3
7
formula
M
C
39H52N3MoBF4
C40H53N4MoBF4
772.61
C40H52N4Mo
684.8
C40H55N3MoBF4Cl3
866.97
C39H55N3MoB2F8
835.42
745.59
cryst syst
space group
a/Å
b/Å
monoclinic
P2(1)/n
13.9050(3)
18.4722(3)
15.5330(3)
90
97.2460(10)
90
3957.88(13)
4
0.379
20697
6963 (0.0496)
1.097
0.0465, 0.0931
monoclinic
P2(1)/c
10.9418(14)
19.072(3)
18.935(2)
90
91.666(2)
18.935(2)
3949.7(9)
4
0.383
20683
6941 (0.0702)
0.903
0.0393, 0.0904
monoclinic
C2/c
11.5888(10)
16.8115(15)
39.321(3)
90
97.910(2)
90
7587.8(11)
8
0.376
15939
4938 (0.0345)
1.306
0.0606, 0.1290
monoclinic
P2(1)/n
10.566(2)
16.005(3)
25.610(6)
90
94.337(14)
90
4318.3(16)
4
0.537
33718
6779 (0.2015)
0.884
0.0533, 0.1038
triclinic
P1h
9.822(3)
12.528(5)
17.506(6)
84.74(4)
88.79(3)
67.36(3)
1979.5(12)
2
c/Å
R/deg
â/deg
γ/deg
U/Å3
Z
µ/mm-1
0.401
17306
6939 (0.0758)
0.923
0.0524, 0.1023
no. of reflns collected
no. of ind reflns (Rint)
goodness of fit on F2
final R indices [I>2σ(I)] R1, wR2
Hexane (8 cm3) was added and the resulting cloudy solution
filtered through Celite. Overnight storage of the filtrate at 4
°C yielded 5 as a red crystalline solid, yield 0.047 g (61%).
[Mo{dC(NHBu t)C(P h )dC(P h )C(NHBu t)}(CNBu t)(η5-C5-
Me5)][BF 4], 6. A solution of 1 (0.200 g, 0.26 mmol) in thf (30
cm3) was stirred over 10 cm3 of a 0.5% sodium-mecury
amalgam for 15 min to give a brown solution, which was
decanted and evaporated to dryness. The resulting solid was
redissolved in diethyl ether (20 cm3), the solution was filtered
through Celite, and then two drops of HBF4‚Et2O were added
to the rapidly stirred solution to precipitate an orange solid.
Brief treatment with ultrasound was used to promote solidi-
fication. This precipitate was isolated by filtration, redissolved
in a mixture of thf (5 cm3) and n-hexane (10 cm3), and then
filtered. Overnight storage of the filtrate at -10 °C gave the
product as red-orange crystals, yield 0.060 g (30%). Crystals
suitable for X-ray diffraction (as a CDCl3 solvate) were grown
from a CDCl3 solution layered with n-hexane.
Cr ysta l Str u ctu r e Deter m in a tion s. The crystal structure
determinations were carried out on a Bruker SMART diffrac-
tometer, that of 1 at 20 °C and those of 2, 3, 6, and 7 in a
nitrogen stream at -100 °C. In all cases graphite-monochro-
mated Mo KR radiation was used. Data correction was
performed with the program SADABS.22 The structures were
solved by direct methods and refined by full-matrix least-
squares techniques against F2 using the programs SHELXS97
and SHELXL97.23 The crystal and intensity data are given in
Table 8. The structures of 1, 6, and 7 contain disordered [BF4]-
counterions, and that of 6 also has a disordered tert-butyl
group. These disordered groups have all been modeled in two
parts, with the sum of the occupancies of the parts constrained
to 1.
Ack n ow led gm en t. We thank the EPSRC for Post-
doctoral Research Associateships (C.J .A. and T.J .P.),
and the University of Bristol for Postgraduate Scholar-
ships (K.M.A. and I.M.B.).
[Mo{dC(NHBu t)C(P h )C(P h )CHNHBu t}(CNBu t)(η5-C5-
Me5)][BF 4]2, 7. A solution of 1 (0.100 g, 0.13 mmol) in thf (20
cm3) was stirred over 10 cm3 of a 0.5% sodium-mercury
amalgam. The resulting orange-brown solution was filtered
through Celite and protonated with a drop of HBF4‚Et2O. The
resulting cloudy orange solution was stirred for 5 min, before
being evaporated to dryness and redissolved in CH2Cl2 (5 cm3).
This was again filtered through Celite, and then the crude
product was precipitated by addition of an excess of diethyl
ether. The resulting yellow powder was isolated by filtration
and crystallized from a concentrated CH2Cl2 solution by
inward vapor diffusion of diethyl ether to give 7 as yellow
crystals, yield 0.042 g (37%).
Su p p or tin g In for m a tion Ava ila ble: Details of the struc-
tural determinations for complexes 1, 2, 3, 6, and 7, including
tables of crystal and intensity collection data, positional and
anisotropic thermal parameters, and all of the bond distances
and angles. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM020313Y
(22) Sheldrick, G. M. SADABS Version 2.03; University of Go¨ttingen,
2001.
(23) (a) Sheldrick, G. M. SHELXS 97; University of Go¨ttingen, 1997.
(b) Sheldrick, G. M. SHELXL 97; University of Go¨ttingen, 1997.