Synthesis, molecular structures, fluxional properties and catalytic activity of a series of alkyne complexes of molybdenum(II) and tungsten(II) containing phosphite donor ligands

Article abstract of DOI:10.1039/a902224d

Treatment of [MoI₂(CO)(NCMe)(η²-R′C₂R″) ₂] with one equivalent of P(OPh)₃ in diethyl ether at room temperature afforded the crystallographically characterised complexes [MoI₂(CO)(NCMe){P(OPh)₃}(η²-R′C ₂R″)] (R′ = R″ = Me or Ph; R′ = Me, R″ = Ph) which have five different ligands attached in a pseudo-octahedral arrangement. Reaction of [MI₂(CO)(NCMe)(η²-R′C₂R″) ₂] with two equivalents of P(OR)₃ in diethyl ether at room temperature gave high yields of the bis(phosphite) complexes [MI₂(CO) {P(OR)₃}₂(η²-R′C ₂R″)] {R = Ph, R′ = Me, R″ = Ph (M = Mo only); M = Mo or W, R = Me, R′ = R″ = Me or Ph (M = Mo only), R′ = Me, R″ = Ph (M = W only); R′ = Me, R″ = Ph (M = W only); R = Et, R′ = R″ = Me or Ph (M = Mo only), R′ = Me, R″ = Ph (M = W only); R = ⁱPr, R′ = R″ = Me or Ph (M = Mo only), R′ = Me, R″ = Ph (M = W only); R = ⁿBu, R′ = R″ = Me, Ph (M = Mo only for both complexes)}. The crystal structures for [MI₂(CO){P(OR)₃}₂(η ²-R′C₂R″)] {M = Mo, R = Me, ⁱPr; R′ = R″ = Me; M = Mo, R = Ph, R′ = Me, R″ = Ph; M = W, R = Et or ⁱPr; R′ = R″ = Me; R′ = Me, R″ = Ph (R = ⁱPr only)} have been determined, and all have trans-phosphite ligands except for M = Mo, R = R′ = R″ = Me which has cis-phosphite groups. The trimerisation of MeC₂Ph by the reaction of [MoI₂(CO)(NCMe)(η²-MeC₂Ph)₂] with P(OⁱPr)₃ to give the crystallographically characterised trimer of MeC₂Ph, 1,2,4-trimethyl-3,5,6-triphenylbenzene, is also described. The fluxional properties of selected complexes have been investigated.

Full text of DOI:10.1039/a902224d

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Synthesis, molecular structures, fluxional properties and catalytic
activity of a series of alkyne complexes of molybdenum(II) and
tungsten(II) containing phosphite donor ligands
Paul K. Baker,*a Michael G. B. Drew,*b Deborah S. Evans,a Archie W. Johansb and
Margaret M. Meehana
a Department of Chemistry, University of Wales, Bangor, Gwynedd, UK LL57 2UW.
E-mail: chs018@bangor.ac.uk
b Department of Chemistry, University of Reading, Whiteknights, Reading, UK RG6 6AD
Received 22nd March 1999, Accepted 11th June 1999
Treatment of [MoI2(CO)(NCMe)(η2-RЈC2RЉ)2] with one equivalent of P(OPh)3 in diethyl ether at room temperature
afforded the crystallographically characterised complexes [MoI2(CO)(NCMe){P(OPh)3}(η2-RЈC2RЉ)] (RЈ = RЉ = Me
or Ph; RЈ = Me, RЉ = Ph) which have five different ligands attached in a pseudo-octahedral arrangement. Reaction of
[MI2(CO)(NCMe)(η2-RЈC2RЉ)2] with two equivalents of P(OR)3 in diethyl ether at room temperature gave high yields
of the bis(phosphite) complexes [MI2(CO){P(OR)3}2(η2-RЈC2RЉ)] {R = Ph, RЈ = Me, RЉ = Ph (M = Mo only);
M = Mo or W, R = Me, RЈ = RЉ = Me or Ph (M = Mo only), RЈ = Me, RЉ = Ph (M = W only); RЈ = Me, RЉ = Ph
(M = W only); R = Et, RЈ = RЉ = Me or Ph (M = Mo only), RЈ = Me, RЉ = Ph (M = W only); R = iPr, RЈ = RЉ = Me or
Ph (M = Mo only), RЈ = Me, RЉ = Ph (M = W only); R = nBu, RЈ = RЉ = Me, Ph (M = Mo only for both complexes)}.
The crystal structures for [MI2(CO){P(OR)3}2(η2-RЈC2RЉ)] {M = Mo, R = Me, iPr; RЈ = RЉ = Me; M = Mo, R = Ph,
RЈ = Me, RЉ = Ph; M = W, R = Et or iPr; RЈ = RЉ = Me; RЈ = Me, RЉ = Ph (R = iPr only)} have been determined,
and all have trans-phosphite ligands except for M = Mo, R = RЈ = RЉ = Me which has cis-phosphite groups.
The trimerisation of MeC2Ph by the reaction of [MoI2(CO)(NCMe)(η2-MeC2Ph)2] with P(OiPr)3 to give the
crystallographically characterised trimer of MeC2Ph, 1,2,4-trimethyl-3,5,6-triphenylbenzene, is also described.
The fluxional properties of selected complexes have been investigated.
In molybdenum() and tungsten() complexes containing
Results and discussion
alkyne ligands the alkyne can act as either a two- or a four-
electron donor.1–3 The importance of this type of complex has
been highlighted by two extensive review articles.4,5 Although a
wide range of halogenocarbonyl alkyne complexes of the types
[MoX2(CO)(NCMe)(η2-RC2RЈ)2] and [MX2(CO)L2(η2-RC2RЈ)]
(M = Mo or W; X = Cl, Br, I; R, RЈ = alkyl, aryl, etc.) have been
prepared,6–14 until our work described herein there are very few
examples containing one phosphine or phosphite ligand.
Umland and Vahrenkamp6 have described the synthesis of the
mono (L) complexes [WI2(CO)2L(η2-HC2But)] (L = PMe3,
AsMe3 or CNBut).
Equimolar quantities of [MoI2(CO)(NCMe)(η2-RЈC2RЉ)2]
(RЈ = RЉ = Me or Ph; RЈ = Me, RЉ = Ph) and P(OPh)3 react in
diethyl ether at room temperature to give the alkyne displaced
products [MoI2(CO)(NCMe){P(OPh)3}(η2-RЈC2RЉ)] 1–3 in
good yield. Complexes 1–3 have been fully characterised by
1
elemental analysis (Table 1), IR (Table 2), H and 31P NMR
spectroscopy (Tables 3 and 4). All three complexes have also
been crystallographically characterised. The complexes are all
very air-sensitive in solution, but can be stored in the solid state
under an inert atmosphere for several months at Ϫ17 ЊC with-
out significant decomposition. Their IR spectra all show weak
nitrile bands and alkyne stretching bands in the expected
positions for these ligands when they are co-ordinated to a
transition-metal centre. The more electron rich alkyne 2-butyne
has the lowest carbonyl stretching band (1995 cmϪ1), whereas
the least electron rich alkyne diphenylacetylene has ν(CO) at
2013 cmϪ1 (see Table 2).
Suitable single crystals for X-ray analysis were grown by
cooling (Ϫ17 ЊC) concentrated diethyl ether solutions of com-
plexes 1–3 for 24 h. The structures are shown in Figs. 1, 2 and 3
respectively and their dimensions are compared in Table 5.
Crystal data are given in Table 6. The differences between the
molecules are in the nature of the alkyne being 2-butyne in 1,
diphenylacetylene in 2 and 1-phenyl-1-propyne in 3. These
changes have made little difference to the geometry of the metal
co-ordination sphere. Each contains a molybdenum atom in a
distorted octahedral environment assuming that the alkyne
occupies one site. There are five different groups bonded to the
metal with the only duplication being two iodides. The carbonyl
In 198815 we described the synthesis and crystal structures
of the bis(alkyne) complexes [WI2(CO)(NCMe)(η2-RC2R)2]
(R = Me or Ph). These have an extensive range of chemistry,5,16
including reactions with phosphite donor ligands. In 198917 we
described the synthesis and crystal structure (for R = RЈ = Me)
of the bis(phosphite) complexes [WI2(CO){P(OR)3}2(η2-
RЈC2RЈ)] (R = Me, Et, iPr or nBu; RЈ = Me or Ph). In this paper
we report the reactions of equimolar quantities of [MoI2-
(CO)(NCMe)(η2-RЈC2RЉ)2] and P(OPh)3 to give the first
mono(phosphite) complexes of the type [MoI2(CO)-
(NCMe){P(OPh)3}(η2-RЈC2RЉ)] (RЈ = RЉ = Me or Ph; RЈ = Me,
RЉ = Ph) which have all been crystallographically characterised.
We also considerably extend the series of bis(phosphite) com-
plexes [MI2(CO){P(OR)3}2(η2-RЈC2RЉ)], including six which
have been crystallographically characterised. The trimerisation
of MeC2Ph from the reaction of [MoI2(CO)(NCMe)(η2-
MeC2Ph)2] with P(OiPr)3 to give the crystallographically charac-
terised arene 1,2,4-trimethyl-3,5,6-triphenylbenzene is also
briefly discussed.
J. Chem. Soc., Dalton Trans., 1999, 2541–2550
2541

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Table 1 Physical and analytical dataa for the phosphite alkyne complexes of molybdenum() and tungsten() 1–18
Analysis (%)
Complex
Colour
Yield (%)
C
H
N
1 [MoI2(CO)(NCMe){P(OPh)3}(η2-MeC2Me)]
2 [MoI2(CO)(NCMe){P(OPh)3}(η2-MePhC2Ph)]
3 [MoI2(CO)(NCMe){P(OPh)3}(η2-MeC2Ph)]
4 [MoI2(CO){P(OPh)3}2(η2-MeC2Ph)]
5 [MoI2(CO){P(OMe)3}2(η2-MeC2Me)]
6 [WI2(CO){P(OMe)3}2(η2-MeC2Me)]
7 [MoI2(CO){P(OMe)3}2(η2-PhC2Ph)]
8 [WI2(CO){P(OMe)3}2(η2-MeC2Ph)]
9 [MoI2(CO){P(OEt)3}2(η2-MeC2Me)]
10 [MoI2(CO){P(OEt)3}2(η2-PhC2Ph)]
11 [WI2(CO){P(OEt)3}2(η2-MeC2Me)]
12 [WI2(CO){P(OEt)3}2(η2-MeC2Ph)]
13 [MoI2(CO){P(OiPr)3}2(η2-MeC2Me)]
14 [MoI2(CO){P(OiPr)3}2(η2-PhC2Ph)]
15 [WI2(CO){P(OiPr)3}2(η2-MeC2Me)]
16 [WI2(CO){P(OiPr)3}2(η2-MeC2Ph)]
17 [MoI2(CO){P(OnBu)3}2(η2-MeC2Me)]
18 [MoI2(CO){P(OnBu)3}2(η2-PhC2Ph)]
Brown
89
82
65
61
81
92
92
66
90
87
83
82
85
84
90
98
66
79
39.2
(38.2)
46.4
(46.2)
42.6
(42.6)
50.2
(49.6)
19.8
(19.4)
17.4
(17.2)
30.8
(31.3)
23.6
(23.2)
26.6
(26.6)
35.5
(36.4)
24.2
(24.0)
29.2
(28.9)
32.6
(32.5)
40.2
(40.6)
29.7
(29.5)
34.1
3.2
(3.1)
3.3
(3.3)
3.4
(3.1)
3.6
(4.3)
3.5
(3.5)
3.2
(3.3)
5.4
(3.5)
3.0
(3.2)
4.6
(4.7)
3.7
(4.5)
4.0
(4.3)
3.9
(4.2)
5.8
(5.7)
5.0
(5.4)
5.3
(5.2)
5.8
1.7
(1.8)
1.8
(1.5)
1.5
(1.7)
—
Light brown
Brown
Brown
Green
—
—
—
—
—
—
—
—
—
—
—
—
—
—
Purple-green
Green
Green
Green
Dark-brown
Green
Green
Green
Brown
Green
Green
(33.7)
37.9
(37.3)
43.9
(5.1)
6.8
(6.4)
5.8
Brown
Brown
(44.2)
(6.1)
a Calculated values in parentheses.
Table 2 IR Dataa (cmϪ1), for the phosphite alkyne complexes of
molybdenum() and tungsten() 1–18
greater in the case of the diphenylacetylene in 2, where the
difference is 0.059 Å than in 1 and 3 where the differences are
0.033, 0.032 and 0.027 Å respectively. The position of the two
carbon atoms trans to I(2) are slightly different with C(21) more
closely trans than C(11) by between 4 and 8Њ. Bond lengths in
the three structures are otherwise unremarkable.
᎐
᎐
᎐
Complex
ν(C᎐N)
ν(C᎐O)
ν(C᎐C)
᎐
᎐
᎐
1
2
2314w, 2287w
2360w, 2341w
2319w, 2225w
1995s
2013s
2000s
1994s
2001s, 1943 (sh)
1989s (br)
2014s, 1968 (sh)
1992s, 1960 (sh) s
1998s, 1970s
2004s, 1979s
1981 (br) s, 1961 (sh)
1986, 1962s (br)
1969s
1591w
1643w
1653w
1637w
1676w
1665w
1654w, 1601w
1656vw
1668w
1608w
1655w
1625vw
1677w
1601w
1654w
1619w
1618w
1601w
It is likely that the reactions of [MoI2(CO)(NCMe)-
(η2-RЈC2RЉ)2] with P(OPh)3 go via an associative mechanism,
since the alkyne can alter its mode of bonding from being a 4-
to a 2-electron donor, upon addition of P(OPh)3. Associative
mechanisms have been previously suggested for this type of
substitution reaction in molybdenum() and tungsten() alkyne
complexes.19,20 It is interesting, that in our previous studies17
refluxing equimolar amounts of [WI2(CO)(NCMe)(η2-PhC2-
Ph)2] and P(OPh)3 in CHCl3 for 48 h afforded the proposed
mono(triphenyl phosphite) complex [WI2(CO){P(OPh)3}-
(η2-PhC2Ph)2] {ν(CO) 2030 cmϪ1}, [WI2(CO){P(OPh)3}2-
(η2-PhC2Ph)] {ν(CO) 1990 cmϪ1} and the starting complex
[WI2(CO)(NCMe)(η2-PhC2Ph)2] {ν(CO) 2090 cmϪ1}. It was
also reported that there was extensive decomposition in these
reactions. By contrast, the reactions described herein using
molybdenum instead of tungsten proceed smoothly to the
alkyne substituted product in an apparently stereoselective
manner. Addition of a second equivalent of P(OPh)3 to
[MoI2(CO)(NCMe){P(OPh)3}(η2-MeC2Ph)] 3 in diethyl ether
eventually gives the crystallographically characterised (Fig.
4) trans-bis(triphenyl phosphite) complex [MoI2(CO)-
{P(OPh)3}2(η2-MeC2Ph)] 4. It is very likely this reaction goes
via initial formation of the cis-complex (see structures of cis-
[MI2(CO){P(OMe)3}2(η2-MeC2Me)] {M = Mo (this work);
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1970s
1955s (br)
1959s
1962s
1964s
a Spectra recorded in CHCl3 as thin films between NaCl plates;
br = broad, s = strong, w = weak.
group is trans to the acetonitrile, the phosphite ligand P(4) is
trans to one iodide I(3), and the alkyne is trans to the other
iodide I(2). It is interesting that in all four cases {two molecules
of 1, together with 2 and 3} the Mo–I(2) bond length is greater
than the Mo–I(3) bond length, no doubt because of the trans
effect of the alkyne. It is possible to conclude that this effect is
2542
J. Chem. Soc., Dalton Trans., 1999, 2541–2550

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Table 3 Proton NMR data (δ, J/Hz)a for the phosphite alkyne complexes of molybdenum() and tungsten() 1–18
Complex
1
2
3
4
5
7.5–7.2 {m, 15 H, P(OPh)3}; 2.9 (s, 6 H, C2CH3); 2.1 (s, 3 H, NCMe)
7.7–7.4 {m, 25 H, P(OPh)3}; 2.1 (s, 3 H, NCMe)
7.2 {m, 15 H, P(OPh)3}; 7.0 (m, 5 H, PhC2CH3); 3.0 (s, 3 H, CH3C2Ph); 2.1 (s, 3 H, NCCH3)
7.25 {m, 30 H, P(OPh)3}; 6.9 (m, 5 H, PhC2CH3); 3.0 (br s, 3 H, CH3C2Ph)
3.9 (d, JP-H = 10.0, 9 H, OCH3); 3.5 (d, JP-H = 10.0, 9 H, OCH3); 3.0 (s, 6 H, C2CH3), cis; 3.6 (t, JP-H = 5.2, 18 H, OCH3); 3.1 (m, 6 H,
C2CH3), trans
6
7
4.0 (d, JP-H = 10.0, 9 H, OCH3); 3.5 (d, JP-H = 10.0, 9 H, OCH3); 2.9 (s, 6 H, CH3C2CH3), cis; 3.6 (t, JP-H = 5.4, 18 H, OCH3); 3.1 (s, 6 H,
CH3C2CH3), trans
7.8–7.6 (m, 10 H, Ph); 3.9 (d, JP-H = 10.0, 9 H, OCH3); 3.7 (d, JP-H = 10.0, 9 H, OCH3), cis; 7.6–7.4 (m, 10 H, Ph); 3.6 (t, JP-H = 5.4, 18 H,
OCH3), trans
8
7.5 (m, 5 H, CH3C2Ph); 3.7 (d, JP-H = 11.9, 9 H, OCH3); 3.4 (d, JP-H = 9.3, 9 H, OCH3); 3.2 (s, 3 H, CH3C2Ph), cis; 7.4 (m, 5 H, CH3C2Ph);
3.5 (m, 18 H, OCH3); 3.0 (s, 3 H, CH3C2Ph), trans
9
3.95 (m, 12 H, OCH2CH3); 3.1 (t, JH-H = 1.0, 6 H, C2CH3); 1.35 (m, 18 H, OCH2CH3), cis; 3.85 (m, 12 H, OCH2CH3); 2.9 (s, 6 H,
C2CH3); 1.15 (t, JH-H = 5.4, 18 H, OCH2CH3), trans
10
11
12
7.6–7.3 (m, 10 H, Ph); 4.15 (m, 12 H, OCH2); 1.3 (m, 18 H, OCH2CH3), cis; 7.3–6.9 (m, 10 H, Ph); 3.95 (m, 12 H, OCH2); 1.15 (m, 18 H,
OCH2CH3), trans
4.3 (m, 12 H, OCH2CH3); 2.9 (s, 6 H, C2CH3); 1.4 (t, JP-H = 7.0, 18 H, OCH2CH3), cis; 4.0 (m, 12 H, OCH2CH3); 3.1 (t, JH-H = 2.1, 6 H,
C2CH3); 1.2 (t, JP-H = 7.0, 18 H, OCH2CH3), trans
7.6–7.4 (m, 5 H, CH3C2Ph); 4.0 (m, 12 H, OCH2CH3); 3.3 (m, 3 H, CH3C2Ph); 1.4 (m, 18 H, OCH2CH3), cis; 7.4–7.2 (m, 5 H, CH3C2Ph);
3.9 (m, 12 H, OCH2CH3); 3.2 (m, 3 H, CH3C2Ph); 1.2 (m, 18 H, OCH2CH3), trans
4.4–4.2 {m, 6 H, OCH(CH3)2}; 3.0 (s, 6 H, C2CH3); 1.9 {m, JP-H = 6.4, 36 H, OCH(CH3)2}
7.5–6.8 (m, 10 H, Ph); 4.7–4.5 {m, 6 H, OCH(CH3)2}; 1.3–1.1 (m, 36 H, OCH(CH3)2)
4.7 {m, 6 H, OCH(CH3)2}; 3.1 (s, 6 H, C2CH3); 1.2 {d, JP-H = 7.7, 36 H, OCH(CH3)2}
7.4 (m, 5 H, CH3C2Ph); 4.7 {m, 6 H, OCH(CH3)2}; 3.2 (s, 3 H, CH3C2Ph); 1.2 {m, 36 H, OCH(CH3)2}
4.2 (m, 12 H, OCH2); 2.9 (s, 6 H, C2CH3); 1.5–1.3 (m, 24 H, OCH2CH2CH2CH3); 0.95 (m, 18 H, CH3)
7.7–7.4 (m, 10 H, Ph); 4.1 (m, 12 H, OCH2); 1.5 (m, 24 H, OCH2CH2CH2CH3); 0.9 (m, 18 H, CH3)
13
14
15
16
17
18
a Spectra recorded in CDCl3 (ϩ25 ЊC) and referenced to SiMe4; br = broad, d = doublet, m = multiplet, s = singlet.
Table 4 31P NMR Data (δ, J/Hz)a for the phosphite alkyne complexes of molybdenum() and tungsten() 1–18
Complex
1
2
134.0 {s, P(OPh)3}
84.1 {s, P(OPh)3}
111.70 {s, P(OPh)3}
127.3 {s, P(OPh3)}, trans
3
4
5
131.4 {d, JP-P = 46.5, P(OMe)3}, cis; 121.6 {d, JP-P = 46.5, P(OMe)3}, cis; 117.1 {s, P(OMe)3}, trans
110.7 {d, JP-P = 29.4, P(OMe)3}, cis; 104.1 {d, JP-P = 29.4, P(OMe)3}, cis; 105.5 {s, P(OMe)3}, trans
126.5 {d, JP-P = 42.2, P(OMe)3}, cis; 118.7 {d, JP-P = 42.2, P(OMe)3}; cis; 114.9 {s, P(OMe)3}, trans
110.3 {d, JP-P = 28.9, P(OMe)3}, cis; 102.2 {d, JP-P = 28.9, P(OMe)3}, cis; 104.1 {s, P(OMe)3}; trans
129.2 {d, JP-P = 47.7, P(OEt)3}, cis; 116.4 {d, JP-P = 47.7, P(OEt)3}, cis; 111.0 {s, P(OEt)3}, trans
123.4 {d, JP-P = 44.0, P(OEt)3}, cis; 114.0 {d, JP-P = 44.0, P(OEt)3}, cis; 110.3 {s, P(OEt)3}, trans
109.4 {d, JP-P = 30.4, P(OEt)3}, cis; 98.7 {d, JP-P = 30.4, P(OEt)3}, cis; 100.5 {s, P(OEt)3}, trans
108.6 {d, JP-P = 34.4, P(OEt)3}, cis; 97.3 {d, JP-P = 34.4, P(OEt)3}, cis; 99.5 {s, P(OEt)3}, trans
109.0 {s, P(OiPr)3}, trans
6
7
8
9
10
11
12
13
14
15
16
17
18
105.5 {s, P(OiPr)3}, trans
94.8 {s, JW-P = 211.0, P(OiPr)3}, trans
94.4 {s, JW-P = 208.2, P(OiPr)3}, trans
127.4 {s, P(OnBu)3}, trans
78.6 {s, P(OnBu)3}, trans
a Spectra recorded in CDCl3 at ϩ25 ЊC, referenced to 85% H3PO4.
M = W (ref. 17)}), which due to the larger “cone angle”21 of
P(OPh)3 rapidly rearranges via a trigonal twist mechanism to
the thermodynamically more stable trans isomer (Fig. 4). The
proposed mechanism for these steps in the addition of 1 and 2
equivalents of P(OPh)3 to [MoI2(CO)(NCMe)(η2-MeC2Ph)2] is
shown in Scheme 1. The mechanism for the reaction of the tung-
sten complexes [WI2(CO)(NCMe)(η2-RC2R)2] with P(ORЈ)3 is
different, and most likely goes via the bis(alkyne) intermediates
RЉ = Ph (M = W only); M = Mo, R = nBu, RЈ = RЉ = Me or Ph}
in high yield. All complexes have been fully characterised by
elemental analysis (C, H and N) (Table 1), IR spectroscopy
(Table 2), 1H and 31P NMR spectroscopy (Tables 3 and 4) and in
selected cases by 13C NMR spectroscopy (Table 7). The crystal
structures of six of the complexes [MI2(CO){P(OR)3}2-
i
(η2-RЈC2RЉ)] {M = Mo, R = Me or Pr, RЈ = RЉ = Me; R = Ph,
RЈ = Me, RЉ = Ph; M = W, R = Et or iPr, RЈ = RЉ = Me;
RЈ = Me, RЉ = Ph} have been determined. The complexes are all
air-sensitive in solution, but can be stored under an inert N2
atmosphere for several months at Ϫ17 ЊC. They are extremely
soluble in CH2Cl2 and CHCl3, and soluble in diethyl ether. The
preparations in this paper differ from the closely related syn-
1
[WI2(CO){P(ORЈ)3}(η2-RC2R)2].17 The H and 31P NMR spec-
tra of 1–3 all conform with the structures shown in Figs. 1–3.
Reaction of [MI2(CO)(NCMe)(η2-RЈC2RЉ)2] with two
equivalents of P(OR)3 in diethyl ether at room temperature
affords high yields of the bis(phosphite) complexes
[MI2(CO){P(OR)3}2(η2-RЈC2RЉ)] 4–18 {M = Mo, R = Ph,
RЈ = Me, RЉ = Ph; M = Mo or W, R = Me, RЈ = RЉ = Me or Ph
(M = Mo only); RЈ = Me, RЉ = Ph (M = W only); R = Et,
RЈ = RЉ = Me or Ph (M = Mo only); RЈ = Me, RЉ = Ph (M = W
only); R = iPr, RЈ = RЉ = Me or Ph (M = Mo only), RЈ = Me,
i
thesis of [WI2(CO){P(OR)3}2(η2-RЈC2RЈ)] (R = Me, Et, Pr or
nBu; RЈ = Me, Ph)17 in that the previous syntheses were carried
out in CH2Cl2, whereas here they are carried out in diethyl
ether. This procedure enabled growth of suitable single crystals
for X-ray analysis.
J. Chem. Soc., Dalton Trans., 1999, 2541–2550
2543

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their atom numbering schemes. The structure of cis-[MoI2-
(CO){P(OMe)3}2(η2-MeC2Me)] 5 is similar to the previously
reported17 structure of the exact tungsten analogue, cis-
[WI2(CO){P(OMe)3}2(η2-MeC2Me)]. It is interesting that once
the mother-liquor was removed from the green crystals of
5 small brown crystals not good enough for X-ray crystal-
lography were grown, which are very likely to be the trans
isomer. This also occurs with the tungsten analogue:17 a green
solution from purple cis gives small green crystals which were
unsuitable for X-ray crystallography.
Dimensions in the structures of complexes 4, 11, 13, 15, 16,
and 5 are listed in Table 5. In 4, 11, 13, 15 and 16 the two
phosphite ligands are mutually trans, while in 5 they are
mutually cis. The five structures with trans-phosphites are all
similar with an alkyne trans to one iodide and the carbonyl
groups trans to the other iodide. However, in all these examples
the structures of the molecules are compatible with C2 sym-
metry, apart from the substituted alkyne, and the carbonyl
group. In 13 and 15 this symmetry is imposed crystallographi-
cally. However in 4, 11 and 16 this is not the case. In 11 there
was positional disorder, but this was not apparent in 4 or 16.
The disorder proved difficult to treat because of overlapping
atoms and the dimensions obtained are somewhat more
inaccurate than is desirable. When the dimensions in Table 5 are
compared, it should be noted that for the molecules without
crystallographically imposed symmetry there are two alterna-
tive ways of numbering, and the comparison of dimensions
may reflect these differences.
Fig. 1 An ORTEP18 diagram showing the structure of [MoI2(CO)-
(NCMe){P(OPh)3}(η2-MeC2Me)] 1 and the atom numbering scheme.
Owing to the disorder it is difficult to draw any detailed
conclusions from these structures, other than to confirm the
connectivity and the relative positions of the donor atoms.
However, it is clear from the dimensions that the disposition of
the alkyne group relative to the trans atom I(2) is not sym-
metrical. Thus the difference between C(11)–M–I(2) and
C(11)–M–I(3) ranges from 15 to 36Њ. The angles subtended at
the metal by the two phosphorus atoms in all structures are
within 10.5Њ of 180Њ, while the angle between the carbonyl
group and I(2) ranges from 158(2) to 168(2)Њ. It is significant
that the disorder between carbonyl groups and alkyne occurs
for both 2-butyne and 1-phenyl-1-propyne indicating that
the phenyl group has little effect on the geometry of the co-
ordination sphere. However, we did not determine a structure
containing diphenylacetylene and the bulk of this ligand may
well have produced a more ordered structure.
Fig. 2 An ORTEP diagram showing the structure of [MoI2(CO)-
(NCMe){P(OPh)3}(η2-PhC2Ph)] 2 and the atom numbering scheme.
In these examples there was no discernible difference in struc-
i
ture between examples when R = Et, Pr or Ph. However, with
R = Me as in 5, a different configuration was found with the
phosphite ligands mutually cis and this is shown in Fig. 5. One
phosphorus atom P(4) is trans to an iodide I(2), and forms a
shorter bond to the metal, 2.469(3) Å, than the phosphorus
atom P(7) trans to carbonyl, 2.516(3) Å. The iodide I(3) trans to
the alkyne group forms a longer bond than I(2) trans to phos-
phorus {2.849(2), 2.823(2) Å}. The dimensions are generally
as expected. Unlike the trans examples, there is no sign of
disorder in this structure. It is interesting that this compound
is isomorphous with the tungsten analogue,17 but it is not
apparent why the phosphite with R = methyl has a different
structure from R = ethyl, isopropyl or phenyl in which the
phosphite groups are trans. It may be that the “cone angle”21
i
of R = Et, Pr or Ph is larger compared to R = Me in these
complexes.
The IR spectra of complexes 5, 7, 8, 9, 10, 11 and 12 all
showed two carbonyl stretching bands, and it is very likely the
higher wavenumber band will be due to that of the cis isomer.
In this case the carbonyl ligand is trans to a strong π-acceptor
phosphite ligand, whereas in the trans-phosphite complexes the
carbonyl group is trans to an iodo-group. The rapidly obtained
IR spectrum (CHCl3) of single crystals of the complex cis-
[MoI2(CO){P(OMe)3}2(η2-MeC2Me)] 5 displayed a single band
at 2001 cmϪ1, due to the cis isomer, whereas a rapidly obtained
Fig. 3 An ORTEP diagram showing the structure of [MoI2(CO)-
(NCMe){P(OPh)3}(η2-MeC2Ph)] 3 and the atom numbering scheme.
Suitable single crystals for X-ray crystallography were gener-
ally grown by cooling (Ϫ17 ЊC) concentrated diethyl ether
solutions of 4, 5, 11, 13, 15 and 16 for 24 h. The molecular
structures of 4, 5, 11, 13 (which is equivalent to the structure of
15 not shown) and 16 are shown in Figs. 4–8, together with
2544
J. Chem. Soc., Dalton Trans., 1999, 2541–2550

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Table 5 Dimensions (bond lengths in Å angles in Њ) in the co-ordination spheres of the metal complexes
1a
1b
2
3
Mo(1)–C(100)
Mo(1)–C(21)
Mo(1)–C(11)
Mo(1)–N(300)
Mo(1)–P(4)
Mo(1)–I(3)
1.979(15)
2.019(12)
2.074(13)
2.218(11)
2.477(4)
2.818(3)
2.851(3)
2.025(14)
2.026(14)
2.032(11)
2.191(11)
2.472(4)
2.821(3)
2.853(3)
1.988(13)
2.046(10)
2.052(11)
2.193(10)
2.471(4)
2.794(3)
2.853(3)
1.983(13)
2.026(13)
1.989(13)
2.223(11)
2.471(4)
2.811(3)
2.839(2)
Mo(1)–I(2)
C(100)–Mo(1)–C(21)
C(100)–Mo(1)–C(11)
C(21)–Mo(1)–C(11)
C(100)–Mo(1)–N(300)
C(21)–Mo(1)–N(300)
C(11)–Mo(1)–N(300)
C(100)–Mo(1)–P(4)
C(21)–Mo(1)–P(4)
C(11)–Mo(1)–P(4)
N(300)–Mo(1)–P(4)
C(100)–Mo(1)–I(3)
C(21)–Mo(1)–I(3)
C(11)–Mo(1)–I(3)
N(300)–Mo(1)–I(3)
P(4)–Mo(1)–I(3)
110.6(6)
71.6(6)
38.4(5)
166.0(5)
83.0(4)
121.0(5)
91.8(4)
89.3(4)
91.8(3)
93.8(3)
87.9(4)
102.2(3)
99.6(3)
83.9(3)
167.83(9)
84.3(4)
161.5(4)
153.7(4)
84.2(3)
78.22(9)
89.66(6)
110.7(5)
73.9(7)
37.0(5)
167.6(5)
81.3(5)
117.9(5)
89.3(4)
92.2(4)
95.5(3)
92.9(3)
90.3(4)
97.7(4)
94.6(3)
85.3(3)
169.52(9)
85.2(4)
162.0(4)
158.5(4)
85.3(3)
79.21(9)
90.32(5)
112.6(4)
75.1(5)
37.6(4)
160.7(4)
85.0(4)
121.7(4)
93.4(4)
88.4(3)
93.2(3)
94.8(3)
84.8(4)
103.3(3)
97.9(3)
83.5(3)
167.92(8)
82.0(3)
160.1(3)
154.5(3)
83.0(3)
76.83(9)
91.10(6)
111.7(5)
72.5(5)
39.2(5)
160.9(5)
86.7(4)
125.6(4)
94.5(4)
84.5(3)
88.6(4)
92.2(3)
85.4(4)
103.4(3)
99.3(4)
85.3(3)
171.68(8)
82.2(4)
159.0(3)
150.7(4)
81.6(3)
78.62(11)
93.10(9)
C(100)–Mo(1)–I(2)
C(21)–Mo(1)–I(2)
C(11)–M(1)–I(2)
N(300)–Mo(1)–I(2)
P(4)–Mo(1)–I(2)
I(3)–Mo(1)–I(2)
11a (M = W)
4 (M = Mo)
a
b
c
13b (M = Mo)
15b (M = W)
16 (M = W)
M(1)–C(21)
M(1)–C(100)
M(1)–C(11)
M(11)–P(4)
M(1)–P(4Ј)c
M(1)–I(2)
1.92(4)
1.96(3)
1.85(5)
2.505(8)
2.523(8)
2.833(5)
2.844(4)
1.987(18)
2.027(17)
2.021(18)
2.497(11)
2.570(11)
2.831(4)
2.009(18)
2.018(17)
2.023(18)
2.495(12)
2.545(11)
2.842(4)
1.99(3)
1.941(19)
2.030(13)
1.991(16)
2.545(4)
2.545(4)
2.891(2)
2.891(2)
1.929(16)
2.079(13)
1.959(12)
2.528(2)
2.528(2)
2.875(1)
2.875(1)
1.961(19)
1.932(19)
2.091(18)
2.511(7)
2.569(6)
2.847(3)
2.890(4)
2.019(17)
1.999(19)
2.496(15)
2.545(16)
2.836(5)
2.891(5)
M(1)–I(2Ј)d
2.883(4)
2.873(4)
C(21)–M(1)–C(100)
C(21)–M(1)–C(11)
C(100)–M(1)–C(11)
C(21)–M(1)–P(4)
C(100)–M(1)–P(4)
C(11)–M(1)–P(4)
C(21)–M(1)–P(4Ј)
C(100)–M(1)–P(4Ј)
C(11)–M(1)–P(4Ј)
P(4)–M(1)–P(4Ј)
C(21)–M(1)–I(2)
C(100)–M(1)–I(2)
C(11)–M(1)–I(2)
P(4)–M(1)–I(2)
P(4Ј)–M(1)–I(2)
C(21)–M(1)–I(2Ј)
C(100)–M(1)–I(2Ј)
C(11)–M(1)–I(2Ј)
P(4)–M(1)–I(2Ј)
P(4Ј)–M(1)–I(2Ј)
I(2)–M(1)–I(2Ј)
115.0(14)
43.0(9)
72.2(15)
98.5(12)
88.1(9)
94.9(15)
85.2(12)
95.5(9)
91.7(15)
173.2(3)
165.5(11)
76.7(9)
148.2(13)
90.2(2)
85.1(2)
83.5(11)
160.9(8)
126.0(13)
84.8(2)
109.2(16)
38.1(6)
106.6(18)
37.8(7)
106(3)
38.6(7)
68(3)
94(3)
86(3)
91(2)
90(3)
96(3)
94(2)
105.1(11)
38.9(7)
66.9(10)
100.8(8)
93(2)
96(2)
83.7(8)
90(2)
108.0(9)
38.1(5)
69.9(8)
94(2)
96.5(9)
95.9(15)
90(2)
86.3(9)
90.3(15)
173.7(1)
178(2)
71.9(6)
141.8(5)
87.7(2)
87.9(2)
90.6(5)
160.5(6)
128.7(5)
87.9(2)
87.7(2)
89.38(4)
110.1(8)
38.7(7)
71.9(7)
85.4(7)
92.6(7)
93.3(6)
105.0(7)
85.8(7)
71.3(16)
101.4(16)
85.0(16)
94.4(16)
81.7(16)
96.2(16)
89.6(16)
176.1(2)
168.5(15)
72.9(14)
143.3(10)
89.9(2)
86.9(2)
92.6(9)
157.7(14)
130.0(9)
91.0(2)
68.8(11)
95.7(14)
88.1(15)
93.2(17)
87.5(14)
92.5(15)
90.2(17)
176.5(3)
172.2(13)
76.8(15)
143.1(10)
91.4(2)
85.4(2)
90.4(9)
162.9(13)
128.1(9)
88.1(2)
91(2)
96.1(6)
174.5(7)
170.9(15)
82(2)
173.7(2)
171.1(8)
72.8(6)
139.6(7)
87.9(2)
87.7(2)
91.2(6)
163.2(6)
129.8(7)
87.7(2)
87.9(2)
90.4(1)
169.43(18)
165.3(6)
80.1(5)
151.7(5)
83.61(14)
85.82(14)
84.4(6)
164.6(5)
121.5(5)
94.03(16)
85.12(14)
86.74(6)
149.2(14)
90.4(3)
84.9(4)
86.9(13)
165(2)
125.0(14)
86.0(4)
90.4(3)
85.8(2)
90.0(2)
85.65(16)
86.5(2)
86.6(1)
90.3(2)
86.6(1)
5
Mo(1)–C(100)
Mo(1)–C(21)
Mo(1)–C(11)
Mo(1)–P(4)
Mo(1)–P(7)
Mo(1)–I(2)
2.010(10)
C(100)–Mo(1)–C(21)
C(100)–Mo(1)–C(11)
C(21)–Mo(1)–C(11)
C(100)–Mo(1)–P(4)
C(21)–Mo(1)–P(4)
C(11)–Mo(1)–P(4)
C(100)–Mo(1)–P(7)
111.7(5)
C(21)–Mo(1)–P(7)
C(11)–Mo(1)–P(7)
P(4)–Mo(1)–P(7)
C(100)–Mo(1)–I(2)
C(21)–Mo(1)–I(2)
C(11)–Mo(1)–I(2)
P(4)–Mo(1)–I(2)
78.9(3)
117.1(4)
90.27(8)
85.2(3)
103.6(3)
103.7(3)
167.03(7)
P(7)–Mo(1)–I(2)
C(100)–Mo(1)–I(3)
C(21)–Mo(1)–I(3)
C(11)–Mo(1)–I(3)
P(4)–Mo(1)–I(3)
P(7)–Mo(1)–I(3)
I(2)–Mo(1)–I(3)
88.43(6)
82.2(4)
161.5(3)
151.2(3)
77.79(10)
88.40(8)
89.27(9)
2.022(9)
2.027(10)
2.469(3)
2.516(3)
2.823(2)
2.849(2)
73.6(5)
38.2(4)
93.9(3)
88.8(3)
88.4(3)
168.7(4)
Mo(1)–I(3)
a Disordered without crystallographic symmetry. Dimensions of one structure only are given. b Disordered with crystallographic symmetry. c P(7) in
complexes 4 and 16. d I(3) in complexes 4 and 16.
J. Chem. Soc., Dalton Trans., 1999, 2541–2550
2545

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Fig. 5 An ORTEP diagram showing the structure of cis-[MoI2(CO)-
{P(OMe)3}2(η2-MeC2Me)] 5 and the atom numbering scheme.
Fig. 4 An ORTEP diagram showing the structure of trans-[MoI2(CO)-
{P(OPh)3}2(η2-MeC2Ph)] 4 and the atom numbering scheme.
O
C
O
C
R'
R'
C
C
C
I
I
C
C
P(OR)3
R"
R'
R"
Mo
Mo
P(OR)3
I
I
C
N
C
N
C
R"
Me
Me
P(OR)3
O
C
R'
O
C
R'
C
C
C
C
I
(RO)3P
trigonal twist
R"
Mo
R"
Mo
I
Fig. 6 An ORTEP diagram showing the structure of trans-[WI2(CO)-
{P(OEt)3}2(η2-MeC2Me)] 11 and the atom numbering scheme.
P(OR)3
P(OR)3
I
P(OR)3
I
120°
Scheme 1 Proposed mechanism for the stepwise reaction of two
equivalents of P(OR)3 with [MoI2(CO)(NCMe)(η2-RЈC2RЉ)2] (R = Ph,
RЈ = Me, RЉ = Ph).
IR (CHCl3) of single crystals of trans-[MoI2(CO){P(OEt)3}2-
(η2-MeC2Me)] 9 showed a single band at 1970 cmϪ1 due to
the trans isomer. The complexes with the larger phosphite
{P(OR)3} ligands, R =iPr, nBu or Ph, all showed only one
carbonyl band in their spectra (Table 2) due to the trans isomer.
This was confirmed by the 31P NMR studies discussed later.
1
The H NMR data (Table 3) of complexes 4–18 generally
conform with the structures of selected complexes shown. In
order to investigate the barrier to 2-butyne rotation of
[MoI2(CO){P(OR)3}2(η2-MeC2Me)] {R = Me 5, or Et 9}
1
variable temperature H NMR studies were carried out. The
Fig. 7 An ORTEP diagram showing the structure of trans-[MoI2-
(CO){P(OiPr)3}2(η2-MeC2Me)] 13 and the atom numbering scheme.
This structure is equivalent to that of trans-[WI2(CO){P(OiPr)3}2-
(η2-MeC2Me)] 15.
1H NMR spectra were obtained from single crystals of the cis
isomers of complexes 5 and 9 dissolved in CDCl3, soon after
dissolution. The 1H NMR spectra of the 2-butyne methyl
groups at different temperatures of 9 are shown in Fig. 9. The
barriers to 2-butyne rotation of 5 and 9 were calculated,22–24
to be ∆G‡ = 54.7 (Tc = 263 K, ∆ν = 34.5 Hz) and 56.9 (Tc = 274
K, ∆ν = 33.6 Hz) kJ molϪ1 respectively. These values are similar
as expected, to that of the previously reported17 crystallo-
graphically characterised tungsten complex, cis-[WI2(CO)-
We have also used the integral ratios in the 1H NMR spectra
of three series of complexes described here to give the cis:trans
isomer ratio of the phosphites in [MI2(CO){P(OR)3}2-
(η2-RЈC2RЉ)]. For the series of 2-butyne complexes,
[MI2(CO){P(OR)3}2(η2-MeC2Me)], the cis:trans isomer ratios
are, 80:20 (R = Me), 40:60 (R = Et) and 0:100 (R = iPr). The
values for the analogous molybdenum and tungsten complexes
are as expected very similar. For the 1-phenyl-1-propyne com-
plexes, [WI2(CO){P(OR)3}2(η2-MeC2Ph)], ratios are 75:25
{P(OMe)3}2(η2-MeC2Me)] which has ∆G‡ = 55.3 kJ molϪ1
.
Since the ligand cone angles21 of P(OR)3 are 107Њ for R = Me,
and 109Њ for R = Et, very similar, it would not be expected that
these values would differ significantly.
2546
J. Chem. Soc., Dalton Trans., 1999, 2541–2550

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J. Chem. Soc., Dalton Trans., 1999, 2541–2550
2547

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(R = Me), 33:67 (R = Et) and 0:100 (R = iPr). The large cone
angle21 for R = iPr is 128Њ, and this pushes the phosphites into a
trans configuration. There is, as expected, an increase in the
proportion of trans isomer in solution as we go across the series
R = Me < Et < iPr ≈ Ph. This is in accord with the IR results,
and is expected on steric grounds.
the arene was grown by cooling (Ϫ17 ЊC) the reaction mixture
for several days. The structure is shown in Fig. 10. The dimen-
sions are as expected. The central phenyl ring is planar within
experimental error with the three substituent phenyl rings
making angles of 87.5, 74.3 and 76.4Њ. We are currently explor-
ing the trimerisation of a wide range of alkynes by these and
related complexes.
In conclusion we have observed how the reactions of
[MI2(CO)(NCMe)(η2-RЈC2RЉ)2] with phosphite ligands are
very dependent on both the metal and the substituents on the
phosphite ligands. The paper also shows the importance of
solvent choice in organometallic reactions. We have also
discovered a new alkyne trimerisation catalyst system, which we
are continuing to study.
The 31P-{1H} NMR data (CDCl3, 25 ЊC) in Table 4 also show
either a mixture of cis (two doublets) and trans (singlet) isomers
in solution for the smaller cone angle21 phosphites, P(OR)3
(R = Me and Et), whereas for the larger phosphite ligands,
n
(R = iPr, Bu or Ph) only a singlet due to the trans isomer is
1
observed. This is in accord with the IR and H NMR results
discussed above.
The 13C NMR data (Table 7) for complexes 8, 12 and 16 all
show alkyne contact carbon resonances at δ > 200, which sug-
gests from Templeton and Ward’s correlation1 of the number of
electrons donated by an alkyne ligand and the alkyne contact
carbon chemical shift that the alkyne is donating four electrons
to the metal in these complexes. This also enables the complexes
to obey the effective atomic number rule.
Experimental
The synthesis and purification of complexes 1–18 were carried
out under an atmosphere of dry nitrogen using standard
vacuum/Schlenk line techniques. The starting materials
[MI2(CO)(NCMe)(η2-RЈC2RЉ)2] (M = W, RЈ = RЉ = Me or Ph;
RЈ = Me, RЉ = Ph;15 M = Mo, RЈ = RЉ = Me or Ph; RЈ = Me,
RЉ = Ph25) were prepared by the published methods. All
chemicals used were purchased from commercial sources. All
solvents used were dried before use.
Finally, preliminary studies of the reaction of [MoI2(CO)-
(NCMe)(η2-MeC2Ph)2] with two equivalents of P(OiPr)3 in
diethyl ether at room temperature gave the trimer 1,2,4-
trimethyl-3,5,6-triphenylbenzene. A suitable single crystal of
Elemental analyses (C, H and N) were recorded on a Carlo
Erba Elemental Analyser MOD 1108 (using helium as a carrier
gas). The IR spectra were recorded on a Perkin-Elmer 1600
1
FTIR spectrophotometer, H, 13C and 31P-{1H} NMR spectra
on a Bruker AC250 NMR spectrometer. The 1H and 13C NMR
spectra were referenced to SiMe4, 31P-{1H} to 85% H3PO4.
Preparations
[MoI2(CO)(NCMe){P(OPh)3}(ꢀ2-MeC2Me)] 1. To a solution
of [MoI2(CO)(NCMe)(η2-MeC2Me)2] (0.5 g, 0.95 mmol) in
Fig. 8 An ORTEP diagram showing the structure of trans-[WI2(CO)-
{P(OiPr)3}2(η2-MeC2Ph)] 16 and the atom numbering scheme.
Fig. 10 An ORTEP diagram showing the structure of 1,2,4-trimethyl-
3,5,6-triphenylbenzene and the atom numbering scheme.
Fig. 9 The 1H NMR spectra for the 2-butyne methyl groups between ϩ20 and Ϫ30Њ for [MoI2(CO){P(OEt)3}2(η2-MeC2Me)] 9.
J. Chem. Soc., Dalton Trans., 1999, 2541–2550
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Table 7 13C NMR Data (δ)a for selected bis(phosphite) alkyne com-
diethyl ether (30 cm3) was added P(OPh)3 (0.29 g, 0.25 cm3, 0.95
mmol) and the solution stirred for 30 min. The resulting brown
solution was filtered over Celite, reduced to half volume and
cooled to Ϫ17 ЊC to yield brown crystals of [MoI2(CO)-
(NCMe){P(OPh)3}(η2-MeC2Me)] 1 suitable for X-ray crystal-
lography. Yield = 0.68 g, 89%.
plexes of molybdenum() and tungsten()
Complex
᎐ ᎐
228.39 (s, CO); 216.93 (s, C᎐C); 216.23 (s, C᎐C); 130.38,
᎐ ᎐
129.14, 128.60, 127.72, 126.48 (m, Ph); 54.00 (s, OMe);
8
Similar reactions of [MoI2(CO)(NCMe)(η2-RЈC2RЉ)2]
(RЈ = RЉ = Ph; RЈ = Me, RЉ = Ph) with an equimolar quantity
of P(OPh)3 in diethyl ether afforded the complexes [MoI2(CO)-
(NCMe){P(OPh)3}(η2-RЈC2RЉ)] 2 and 3, which were also
crystallographically characterised. Single crystals for X-ray
crystallography were grown by cooling (Ϫ17 ЊC) concentrated
diethyl ether solutions of 2 and 3.
25.52 (s, MeC2Ph)
᎐ ᎐
228.26 (s, CO); 217.99 (s, C᎐C); 216.13 (s, C᎐C); 130.23,
᎐ ᎐
12
130.08, 129.14, 129.07, 128.34, 127.83, 126.35 (m,
PhC2Me); 62.65 (s, OCH2CH3); 25.28 (s, MeC2Ph); 16.07
(s, OCH2CH3)
᎐ ᎐
227.85 (s, CO); 218.67 (s, C᎐C); 215.53 (s, C᎐C); 130.25,
᎐ ᎐
16
129.87, 129.36, 128.94, 128.13, 127.86, 127.20 (m,
PhC2Me); 70.99 (s, OCHMe2); 25.36 (s, MeC2Ph); 23.87
(s, OCHMe2)
[MoI2(CO){P(OPh)3}2(ꢀ2-MeC2Ph)] 4. To a solution of
[MoI2(CO)(NCMe)(η2-MeC2Ph)2] (0.503 g, 0.772 mmol) in
diethyl ether (30 cm3) was added P(OPh)3 (0.40 cm3, 0.479 g,
1.554 mmol), and the solution stirred for 30 min. The resulting
dark brown solution was filtered over Celite, the solvent volume
reduced to half volume (15 cm3) in vacuo and cooled to Ϫ17 ЊC
to yield single crystals of [MoI2(CO){P(OPh)3}2(η2-MeC2Ph)]
a Spectra recorded in CDCl3 (ϩ25 ЊC) and referenced to SiMe4.
parameters. Hydrogen atoms were included in geometric
positions and given thermal parameters equivalent to 1.2 times
those of the atoms to which they were attached. Absorption
corrections were carried out using the DIFABS program.28 The
structures were then refined using SHELXL.29 All calculations
were carried out on a Silicon Graphics R4000 Workstation at
the University of Reading.
4
suitable for X-ray crystallography. Yield of pure
product = 0.525 g, 61%.
[WI2(CO){P(OiPr)3}2(ꢀ2-MeC2Me)] 15. To a solution of
[WI2(CO)(NCMe)(η2-MeC2Me)2] (2.053 g, 3.339 mmol) in
diethyl ether (25 cm3) was added P(OiPr)3 (1.65 cm3, 1.391 g,
6.678 mmol) and the solution was stirred for 30 min. The
resulting dark green solution was filtered over Celite, the
solvent reduced to minimum volume (5 cm3) in vacuo and
cooled to Ϫ17 ЊC to yield green single crystals of [WI2(CO)-
{P(OiPr)3}2(η2-MeC2Me)] 15 suitable for X-ray crystallography.
Yield of pure product = 2.813 g, 90%.
For complex 1 there were two molecules in the asymmetric
unit. Alternative structures were refined with reversed co-
ordinates and that with the lowest R value is reported. In 3 a
solvent acetone molecule was located together with a water
molecule. These solvent molecules were refined with 50%
occupancy. In 4 the structure was disordered. All atoms apart
from the carbonyl and the 1-phenyl-1-propyne were consistent
with a non-crystallographic twofold axis. It was possible that
these two groups were disordered over two sites but no satis-
factory disordered model could be found (unlike in 11, see
below). It proved necessary however to refine the phenyl of the
alkyne as a rigid group. There was high thermal motion in the
structure and oxygen and carbon atoms were refined with
isotropic thermal parameters. Complex 11 contained three
molecules in the asymmetric unit. The structure was close to
C2/c with one molecule in an eightfold general position and one
in fourfold position with an imposed twofold axis but attempts
to refine in this space group proved unsuccessful. A solution in
Cc was thus sought with three independent molecules in the
asymmetric unit. As in 4 the structures were consistent with
twofold symmetry apart from the carbonyl and 2-butyne
moieties which were each disordered over two sites. This was
treated by refining two disordered overlapping positions for
each moiety. Each group was given 50% occupancy in each of
two positions and the distances in each co-ordinated group
were constrained. The refined model therefore had approximate
twofold symmetry. Only the W, I and P atoms were refined
isotropically. There were several large peaks in the Fourier-
difference map, but all were very close to tungsten or iodine
atoms. Complexes 13 and 15 were isomorphous and treated
similarly. In both cases there was considerable doubt as to the
correct space group but solutions were eventually found in
orthorhombic P21212 with merohedral (h, k, l and k, h, l) twin-
ning. The 2-butyne and the carbonyl group were disordered
over two positions, but in this case, unlike 4 and 11, the metal
occupied a crystallographic twofold axis and the 2-butyne and
carbonyl group occupied equivalent positions relative to this
twofold axis. The superimposed carbonyl and 2-butyne were
each refined with 50% occupancy with constrained dimensions
and thermal parameters. The W, I and P atoms were refined
anisotropically. In 16 the structure occupied a twofold axis with
concomitant disorder between the carbonyl group and the 1-
phenyl-1-propyne. This was treated by distance constraints and
both groups were given 50% occupancy. The structure of the
arene trimer was treated in the default manner, but of course no
absorption correction proved necessary.
Similar reactions of [MI2(CO)(NCMe)(η2-RЈC2RЉ)2] with
two mole equivalents of P(OR)3 in diethyl ether at room tem-
perature gave the complexes 5–14 and 16–18. Suitable single
crystals for X-ray analysis for 5, 11, 13, 16 were grown by
cooling concentrated diethyl ether solutions of them to Ϫ17 ЊC
for 24 h.
Reaction of [MoI2(CO)(NCMe)(ꢀ2-MeC2Ph)2] wtih two
equivalents of P(OiPr)3
To a solution of [MoI2(CO)(NCMe)(η2-MeC2Ph)2] (0.528 g,
0.811 mmol) in diethyl ether (30 cm3) was added P(OiPr)3 (0.4
cm3, 0.338 g, 1.621 mmol) and the solution stirred for 30 min.
The resultant dark brown solution was filtered over Celite and
solvent volume reduced in vacuo to 10 cm3. On cooling to
Ϫ17 ЊC for several days single crystals of 1,2,4-trimethyl-3,5,6-
triphenylbenzene were formed. To date, attempts to obtain
sufficient samples of the trimerised product for analyses other
than the crystal structure have been unsuccessful. However, the
synthesis of the mono(triisopropyl phosphite) complex [MoI2-
(CO)(NCMe){P(OiPr)3}(η2-MeC2Ph)] is under investigation, so
as to determine its catalytic ability towards the trimerisation of
alkynes.
X-Ray crystallography
Crystal data for complexes 1, 2, 3, 4, 5, 11, 13, 15, 16 and 1,2,4-
trimethyl-3,5,6-triphenylbenzene are given in Table 6, together
with refinement details. Data for all crystals were collected at
293(2) K with Mo-Kα radiation (λ 0.71073 Å) using the MAR-
research Image Plate System. The default measurement and
refinement procedure is presented first while variations for spe-
cific compounds are reported later. Each crystal was positioned
70 mm from the Image Plate. Ninety five frames were measured
at 2Њ intervals with a counting time of 2 min. Data analyses
were carried out with the XDS program.26 The structures were
solved using direct methods with the SHELXS 86 program.27
The non-hydrogen atoms were refined with anisotropic thermal
J. Chem. Soc., Dalton Trans., 1999, 2541–2550
2549

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13 G. R. Clark, A. J. Nielson, A. D. Rae and C. E. F. Rickard, J. Chem.
CCDC reference number 186/1509.
See http://www.rsc.org/suppdata/dt/1999/2541/ for crystallo-
graphic files in .cif format.
Soc., Dalton Trans., 1994, 1783.
14 A. Mayr, C. M. Bastos, N. Daubenspeck and G. A. McDermott,
Chem. Ber., 1992, 125, 1583.
15 E. M. Armstrong, P. K. Baker and M. G. B. Drew, Organometallics,
1988, 7, 319.
16 P. K. Baker, Chem. Soc. Rev., 1998, 27, 125 and refs. therein.
17 P. K. Baker, E. M. Armstrong and M. G. B. Drew, Inorg. Chem.,
1989, 28, 2406.
18 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
Acknowledgements
M. M. M. and D. S. E. thank the EPSRC for Research Student-
ships. We also thank the EPSRC and the University of Reading
for funds for the image plate system.
19 S. R. Allen, P. K. Baker, S. G. Barnes, M. Green, L. Trollope,
L. Manojlovic-Muir and K. W. Muir, J. Chem. Soc., Dalton Trans.,
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20 R. S. Herrick, D. M. Leazer and J. L. Templeton, Organometallics,
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21 C. A. Tolman, Chem. Rev., 1977, 77, 313.
22 H. S. Gutowsky and C. H. Holm, J. Chem. Phys., 1956, 25, 1228.
23 C. E. Holloway, G. Hulley, B. F. G. Johnson and J. Lewis, J. Chem.
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24 A. Allerhand, H. S. Gutowsky, J. Jonas and R. A. Meinzer, J. Am.
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25 N. G. Aimeloglou, P. K. Baker, M. M. Meehan and M. G. B. Drew,
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26 W. Kabsch, J. Appl. Crystallogr., 1988, 21, 916.
27 SHELXS 86, G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46,
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