Reactivity of [M(CO)4(nbd)] (M = Cr or Mo; nbd = norbornadiene) toward (Ph2PN)C(Ph)[N(SiMe3)2] and C6H4{C[N(SiMe3)2]-(NPPh 2)}2-1,4

Article abstract of DOI:10.1039/a607373e

The interaction of (Ph₂PN)C(Ph)[N(SiMe₃)₂] with 1 equivalent of [M(CO)₄(nbd)] (M = Cr or Mo, nbd = norbornadiene) in diethyl ether gave cis-[M(CO)₄{(Me₃SiN)C(Ph)(NHPPh₂}] (M = Cr 1 or Mo 2) in good yield. The interaction of C₆H₄{C(NPPh₂)[N(SiMe₃) ₂]}₂-1,4 with 2 equivalents of [M(CO)₄(nbd)] (M = Cr or Mo) in tetrahydrofuran gave the symmetric dimer cis-[{M(CO)₄} {(Ph₂PNH)(Me₃SiN)CC₆H₄C(NSiMe ₃)(NHPPh₂)}] (M = Cr 3 or Mo 4) in moderate yield. However, in diethyl ether, this reaction (M = Mo) gave the unsymmetric cis-[(OC)₄Mo{(Ph₂PNH)(Me₃SiN)CC ₆H₄C[N(SiMe₃)₂](NPPh ₂)}Mo(CO)₅] 5 in moderate yield. Compounds 1-5 have been fully characterized by analytical and spectroscopic methods and the structures of 3 and 5 have been established by X-ray crystallography. A 1,3-silyl shift mechanism has been proposed for the formation of the products. The NH proton of the bidentate iminophosphine ligand undergoes facile deuterium exchange with D₂O at ambient temperature.

Full text of DOI:10.1039/a607373e

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Reactivity of [M(CO)4(nbd)] (M = Cr or Mo; nbd = norbornadiene)
toward (Ph2PN)C(Ph)[N(SiMe3)2] and C6H4{C[N(SiMe3)2]-
(NPPh2)}2-1,4
Wai-Kwok Wong,*,a Chaode Sun,a Tao J iang,a Wing-Tak Wong,b Feng Xuec and
Thomas C. W. Mak c
a
Department of Chemistry, Hong Kong Baptist University, Kowloon, Hong Kong
b Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
c Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
The interaction of (Ph2PN)C(Ph)[N(SiMe3)2] with 1 equivalent of [M(CO)4(nbd)] (M = Cr or Mo,
nbd = norbornadiene) in diethyl ether gave cis-[M(CO)4{(Me3SiN)C(Ph)(NHPPh2}] (M = Cr 1 or Mo 2) in good
yield. The interaction of C6H4{C(NPPh2)[N(SiMe3)2]}2-1,4 with 2 equivalents of [M(CO)4(nbd)] (M = Cr or Mo) in
tetrahydrofuran gave the symmetric dimer cis-[{M(CO)4}{(Ph2PNH)(Me3SiN)CC6H4C(NSiMe3)(NHPPh2)}]
(M = Cr 3 or Mo 4) in moderate yield. However, in diethyl ether, this reaction (M = Mo) gave the unsymmetric
cis-[(OC)4Mo{(Ph2PNH)(Me3SiN)CC6H4C[N(SiMe3)2](NPPh2)}Mo(CO)5] 5 in moderate yield. Compounds 1–5
have been fully characterized by analytical and spectroscopic methods and the structures of 3 and 5 have been
established by X-ray crystallography. A 1,3-silyl shift mechanism has been proposed for the formation of the
products. The NH proton of the bidentate iminophosphine ligand undergoes facile deuterium exchange with D2O
at ambient temperature.
Phosphorus–nitrogen compounds are π-electron-rich with
unusual properties.1 This has led to a considerable interest
in their syntheses2 and their co-ordination chemistry toward
transition metals.3 The co-ordination chemistry of (Ph2-
PN)C(Ph)[N(SiMe3)2]3,4 and C6H4{C(NPPh2)[N(SiMe3)2]}2-
1,45 have been briefly examined recently. Herein we report
the results of the interaction of [M(CO)4(nbd)] (M = Cr or
Mo; nbd = 2-norbornadiene = bicyclo[2.2.1]hepta-2,5-diene)
with (Ph2PN)C(Ph)[N(SiMe3)2] and C6H4{C(NPPh2)-
[N(SiMe3)2]}2-1,4.
M = Mo 2. When [Mo(CO)4(nbd)] was allowed to react with
1 equivalent of (Ph2PN)C(Ph)[N(SiMe3)2] in diethyl ether for 2
d at room temperature, subsequent work-up gave yellow crystals
of stoichiometry Mo(CO)4(C22H25N2SiP)ؒH2O, 2ؒH2O, in good
yield (70%) after recrystallization from a diethyl ether–hexane
mixture. Compound 2 exhibited similar IR and 13C-{1H} NMR
absorption patterns to those of 1. In the carbonyl region there
are four absorptions at 2012s, 1908vs, 1876vs and 1834s cmϪ1
in the IR spectrum (KBr); and three doublets at δ 208.7
(JP᎐CO = 9.8), 217.0 (36.6) and 220.7 (8.5 Hz) in the 13C-{1H}
NMR spectrum for the four terminal carbonyls. The IR spec-
trum also contains an absorption at 3356s cmϪ1 indicating the
presence of a NH group. The 31P-{1H} NMR spectrum in C6D6
exhibited a singlet at δ 89.6 for the PPh2 group. Other than the
phenyl resonances, the 1H NMR spectrum shows a doublet and
a singlet of relative intensity 1:9 at δ 5.79 (JP᎐NH = 4.6 Hz) and
0.15 for the NH and SiMe3 protons, respectively, and the 13C-
{1H} NMR spectrum a doublet and a singlet at δ 169.9
Results and Discussion
Preparation of cis-[M(CO)4{(Me3SiN)C(Ph)(NHPPh2)}]
M = Cr 1. When [Cr(CO)4(nbd)] was allowed to react with 1
equivalent of (Ph2PN)C(Ph)[N(SiMe3)2] in diethyl ether for 2 d
at room temperature, subsequent work-up gave yellow crystals
of stoichiometry Cr(CO4)(C22H25N2SiP) 1 in good yield (75%)
after recrystallization from a diethyl ether–hexane mixture. In
the carbonyl region, compound 1 exhibits four absorptions at
2002s, 1900vs, 1880vs and 1822s cmϪ1 in the IR spectrum
(KBr), and three doublets at δ 220.0 (JP᎐CO = 14.7), 227.7 (2.5)
and 228.8 (13.4 Hz) in the 13C-{1H} NMR spectrum for the four
terminal carbonyls. The IR and 13C-{1H} NMR absorption pat-
terns are indicative of a cis-Cr(CO)4L(LЈ) complex. The IR
spectrum also contains an absorption at 3352s cmϪ1 indicating
the presence of a NH group. The 31P-{1H} NMR spectrum in
C6D6 exhibited a singlet at δ 112.0 for the PPh2 group. The
positive increase in its chemical shift relative to the free ligand
(from δ 37.4 to 112.0) is characteristic of chelate-ring
formation.6 In addition to the phenyl resonances, the 1H NMR
spectrum also contains a doublet and a singlet of relative inten-
sity 1:9 at δ 5.90 (JP᎐NH = 6.3 Hz) and 0.17 for the NH and
SiMe3 protons, respectively, and the 13C-{1H} NMR spectrum
(JP᎐NC = 18.2 Hz) and 1.6 for the C᎐N carbon and the SiMe
᎐
3
carbons, respectively. The low-resolution mass spectrum
(electron-impact mode) exhibited the parent peak (M for 98Mo)
at m/z 586. The spectroscopic data for 2 are very similar to those
of 1 and thus structure A can also be assigned to 2.
Preparation of cis-[{M(CO)4}{(Ph2PNH)(Me3SiN)CC6H4C-
(NSiMe3)(NHPPh2)}]
M = Cr 3. When C6H4{C(NPPh2)[N(SiMe3)2]}2-1,4 was
allowed to react with 2 equivalents of [Cr(CO)4(nbd)] in tetra-
hydrofuran for 16 h at room temperature, subsequent work-up
gave yellow crystals of stoichiometry [Cr(CO)4]2(C38H44N4-
Si2P2)ؒ2CH2Cl2, 3ؒ2CH2Cl2, in good yield (50%) after recrystal-
exhibits a doublet and a singlet at δ 169.7 and 1.4 for the C᎐N
᎐
carbon and the SiMe3 carbons, respectively. Based on the above
spectroscopic data, structure A can be assigned to 1 and was
confirmed by an X-ray diffraction study.7
J. Chem. Soc., Dalton Trans., 1997, Pages 693–698
693

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group P(1) co-ordinated to each of the two Cr(CO)4 moieties
forming two five-membered rings. The geometry of the chro-
mium centres is approximately octahedral with the Cr᎐C dis-
tances of the two Cr(CO)4 moieties showing the expected pat-
tern for a cis-Cr(CO)4L2 complex where L is a poorer π acid
than CO. The Cr–C distances of the two mutually trans-
carbonyls are 1.889(8) and 1.874(8) Å for Cr(1)–C(2) and Cr(1)–
C(3), respectively, slightly longer than the 1.821(7) and
1.844(8) Å for the carbonyls trans to the imino N(1) and phos-
phino P(1) groups, respectively.
Table 1 Selected bond lengths (Å) and angles (Њ) for compound 3
Cr(1)᎐P(1)
Cr(1)᎐C(1)
Cr(1)᎐C(3)
C(1)᎐O(1)
C(3)᎐O(3)
P(1)᎐N(2)
N(2)᎐C(20)
P(1)᎐C(11)
2.291(2)
1.821(7)
1.874(8)
1.163(9)
1.154(10)
1.720(5)
1.373(7)
1.809(6)
Cr(1)᎐N(1)
Cr(1)᎐C(2)
Cr(1)᎐C(4)
C(2)᎐O(2)
C(4)᎐O(4)
N(1)᎐C(20)
P(1)᎐C(5)
2.214(5)
1.889(8)
1.844(8)
1.143(10)
1.155(9)
1.281(8)
1.817(7)
Within the tetradentate bridging iminophosphine ligand the
P(1)᎐N(2) bond length of 1.720(5) Å is in the normal range for
a phosphorus–nitrogen single bond. The C(20)᎐N(1) and
C(20)᎐N(2) distances of 1.281(8) and 1.373(7) Å, respectively,
are intermediate between those expected for single (1.46 Å) and
double (1.26 Å) bonds indicating some delocalization about the
N᎐C᎐N framework. The delocalization is also reflected in the
P(1)᎐N(2)᎐C(20) bond angle of 117.7(4)Њ which deviates sig-
nificantly from that expected for a tetrahedral sp3 nitrogen atom
and is closer than for a sp2 nitrogen atom. Similar observations
have been made for related palladium,5 chromium 7 and rhodium
complexes.3 The SiMe3 groups of the imino groups and the
CH2Cl2 solvent molecules are disordered.
C(1)᎐Cr(1)᎐C(2)
C(1)᎐Cr(1)᎐C(4)
C(1)᎐Cr(1)᎐P(1)
C(2)᎐Cr(1)᎐C(4)
C(2)᎐Cr(1)᎐P(1)
C(3)᎐Cr(1)᎐N(1)
C(4)᎐Cr(1)᎐N(1)
N(1)᎐Cr(1)᎐P(1)
N(1)᎐C(20)᎐N(2)
93.9(3)
88.1(3)
90.0(2)
87.1(3)
93.2(2)
91.7(3)
102.2(3)
79.7(1)
122.0(5)
C(1)᎐Cr(1)᎐C(3)
C(1)᎐Cr(1)᎐N(1)
C(2)᎐Cr(1)᎐C(3)
C(2)᎐Cr(1)᎐N(1)
C(3)᎐Cr(1)᎐C(4)
C(3)᎐Cr(1)᎐P(1)
C(4)᎐Cr(1)᎐P(1)
C(20)᎐N(1)᎐Si(1)
P(1)᎐N(2)᎐C(20)
88.4(3)
169.7(3)
175.8(3)
86.7(3)
89.5(3)
90.3(2)
178.1(2)
126.9(4)
117.7(4)
M = Mo 4. When C6H4{C(NPPh2)[N(SiMe3)2]}-1,4 was
allowed to react with 2 equivalents of [Mo(CO)4(nbd)] in tetra-
hydrofuran for 16 h at room temperature, subsequent work-up
gave yellow crystals of stoichiometry [Mo(CO)4]2(C38H44N4-
Si2P2) 4 in good yield (55%) after recrystallization from
a dichloromethane–diethyl ether mixture. Compound 4 exhib-
ited similar absorption patterns to those of 3. In the carbonyl
region there are five absorptions at 2023s, 1920vs, 1877vs, 1843s
and 1827vs cmϪ1 in the IR spectrum (KBr) and three doublets
at δ 207.6 (JP᎐CO = 9.8), 216.2 (36.6) and 220.5 (8.6 Hz) in the
13C-{1H} NMR spectrum for the terminal carbonyl groups of
the two Mo(CO)4 moieties. The IR spectrum also contains an
absorption at 3361m cmϪ1 indicating the presence of a NH
group. The 31P-{1H} NMR spectrum in CDCl3 exhibited only a
singlet at δ 89.5 indicating the presence of two equivalent PPh2
Fig. 1 Perspective view of the molecular structure of compound 3
1
groups. In addition to the phenyl resonances, the H NMR
lization from a dichloromethane–diethyl ether mixture. In the
carbonyl region compound 3 exhibits four absorptions at 2012s,
1898vs, 1884vs (sh) and 1840vs cmϪ1 in the IR spectrum (KBr),
and a doublet, a broad singlet and a doublet at δ 219.9
(JP᎐CO = 14.6), 227.3 and 228.5 (JP᎐CO = 13.4 Hz), respectively, in
the 13C-{1H} NMR spectrum for the terminal carbonyl groups
of the two Cr(CO)4 moieties. The IR and the 13C-{1H} NMR
absorption patterns of 3 are similar to those of 1. This suggests
that the two Cr(CO)4 moieties adopt a cis-Cr(CO)4L(LЈ) con-
figuration. The IR spectrum also exhibited an absorption at
3348w cmϪ1 indicating the presence of a NH group. The 31P-
{1H} NMR spectrum in C6D6 contains only a broad singlet at δ
112.3 for the PPh2 groups indicating the formation of two
equivalent chelating rings. In addition to the phenyl resonances,
the 1H NMR spectrum has two broad singlets of relative inten-
sity 2:18 at δ 6.02 and 0.24 for the NH and SiMe3 protons,
respectively, and the 13C-{1H} NMR spectrum a doublet and a
spectrum in CDCl3 reveals two broad singlets of relative inten-
sity 2:18 at δ 6.15 and 0.13 for the NH and SiMe3 protons,
respectively, and the 13C-{1H} NMR spectrum a doublet and a
broad singlet at δ 167.5 (JP᎐NC = 18.3 Hz) and 4.1 for the C᎐N
᎐
carbons and the SiMe3 carbons, respectively. The low-
resolution mass spectrum (FAB, positive ion mode) exhibited
the parent peak (M + 1) at m/z 1095. Thus, based on the above
spectroscopic data, structure B can also be assigned to 4.
Preparation of cis-[(OC)4Mo{(Ph2PNH)(Me3SiN)CC6H4C-
[N(SiMe3)2](NPPh2)}Mo(CO)5] 5
When C6H4{C(NPPh2)[N(SiMe3)2]}2-1,4 and [Mo(CO)4(nbd)]
were allowed to react in a 1:2 molar ratio in diethyl ether for 16
h at room temperature, subsequent work-up gave yellow crys-
tals of stoichiometry Mo2(CO)9(C41H52N4Si3P2)ؒH2O, 5ؒH2O, in
good yield (60%) after recrystallization from a diethyl ether–
hexane mixture. Crystals of 5ؒ0.5C6H14 suitable for X-ray
diffraction study were grown from a solution of hexane
and the structure was established. A perspective drawing of
5 is shown in Fig. 2. Selected bond lengths and angles given in
broad singlet at δ 167.9 (JP᎐NC = 26.7 Hz) and 4.3 for the C᎐N
᎐
carbons and the SiMe3 carbons, respectively. The low-
resolution mass spectrum (FAB, positive-ion mode) exhibited
the M + 1 peak at m/z 1003. Based on the above spectroscopic
data, a symmetric dimer with structure B can be assigned to 3.
The structure of compound 3 was confirmed by an X-ray
diffraction study. Suitable crystals were grown from a dichloro-
methane–diethyl ether mixture as a dichloromethane solvate,
3ؒ2CH2Cl2. A perspective drawing of 3 is shown in Fig. 1.
Selected bond lengths and angles are given in Table 1. The
structure is consistent with the spectroscopic data. The dimeric
species is centrosymmetric and the ligand acts in a bridging
bidentate mode with the imino group N(1) and the phosphino
Table 2. The structure shows that one of the two ᎐NPPh
᎐
2
groups of the symmetric ligand C6H4{C(NPPh2)[N(SiMe3)2]}2-
1,4 has been transformed into a HNPPh2 group; and the
resultant unsymmetric ligand, (Ph2PNH)(Me3SiN)CC6H4C-
[N(SiMe3)2](NPPh2), acts as a tridentate bridge having N(2)
and P(1) of the NHPPh2 group co-ordinated to the Mo(CO)4
moiety forming a five-membered ring, and P(2) of the ᎐NPPh
᎐
2
group co-ordinated to the Mo(CO)5 moiety. The geometry of
the two molybdenum centres is approximately octahedral with
694
J. Chem. Soc., Dalton Trans., 1997, Pages 693–698

View Article Online
Fig. 2 Perspective view of the molecular structure of compound 5
trans to the phosphino P(2) group is slightly shorter than the
Mo᎐C distances of the four mutually trans-carbonyls which
range from 2.01(2) to 2.07(2) Å.
Table 2 Selected bond lengths (Å) and angles (Њ) for compound 5
Mo(1)᎐P(1)
Mo(1)᎐C(1)
Mo(1)᎐C(3)
Mo(2)᎐P(2)
Mo(2)᎐C(6)
Mo(2)᎐C(8)
C(1)᎐O(1)
C(3)᎐O(3)
C(5)᎐O(5)
C(7)᎐O(7)
C(9)᎐O(9)
P(2)᎐N(3)
2.469(3)
2.03(1)
2.02(1)
2.555(4)
2.01(2)
2.03(2)
1.13(1)
1.15(1)
1.14(1)
1.13(1)
1.11(2)
1.677(10)
1.32(1)
1.40(1)
1.81(1)
1.84(1)
Mo(1)᎐N(2)
Mo(1)᎐C(2)
Mo(1)᎐C(4)
Mo(2)᎐C(5)
Mo(2)᎐C(7)
Mo(2)᎐C(9)
C(2)᎐O(2)
C(4)᎐O(4)
C(6)᎐O(6)
C(8)᎐O(8)
P(1)᎐N(1)
2.345(8)
1.94(1)
1.95(1)
2.04(1)
2.00(1)
2.07(2)
1.16(1)
1.17(1)
1.15(2)
1.12(2)
1.727(8)
1.38(1)
1.27(1)
1.84(1)
1.85(1)
Delocalization about the N᎐C᎐N framework of the HNPPh2
group is observed and reflected by the C(10)᎐N(1) and
C(10)᎐N(2) distances of 1.38(1) and 1.32(1) Å, respectively, and
the P(1)᎐N(1)᎐C(10) bond angles of 119.8(7)Њ which is typical
of a sp2 nitrogen atom. For the unidentate ᎐NPPh group the
᎐
2
geometry of N(4) of the N(SiMe3)2 group is approximately tri-
gonal planar with bond angles ranging from 114.8(8), 121.9(8)
and 122.4(6)Њ for Si(2)᎐N(4)᎐C(17), Si(3)᎐N(4)᎐C(17) and
Si(2)᎐N(4)᎐Si(3), respectively. This suggests that the lone pair
on N(4) has primarily p character and the right symmetry to
interact with the neighbouring empty π* orbital. This p–π*
interaction is reflected in the C(17)᎐N(4) distance of 1.40(1) Å.
The spectroscopic data for compound 5 are consistent with
its solid-state structure. The IR spectrum (KBr) in the carbonyl
region exhibited absorptions at 2068m, 2016m, 1940s (br),
1908vs, 1878s and 1830s cmϪ1. The IR spectrum also showed
N(1)᎐C(10)
N(3)᎐C(17)
P(1)᎐C(18)
P(2)᎐C(30)
N(2)᎐C(10)
N(4)᎐C(17)
P(1)᎐C(24)
P(2)᎐C(36)
C(1)᎐Mo(1)᎐C(2)
C(1)᎐Mo(1)᎐C(4)
C(1)᎐Mo(1)᎐P(1)
C(2)᎐Mo(1)᎐C(4)
C(2)᎐Mo(1)᎐P(1)
C(3)᎐Mo(1)᎐N(2)
C(4)᎐Mo(1)᎐N(2)
N(2)᎐Mo(1)᎐P(1)
C(5)᎐Mo(2)᎐C(7)
C(5)᎐Mo(2)᎐C(9)
C(6)᎐Mo(2)᎐C(7)
C(6)᎐Mo(2)᎐C(9)
C(7)᎐Mo(2)᎐C(8)
C(7)᎐Mo(2)᎐P(2)
C(8)᎐Mo(2)᎐P(2)
P(1)᎐N(1)᎐C(10)
Mo(1)᎐N(2)᎐Si(1)
C(10)᎐N(2)᎐Si(1)
N(3)᎐C(17)᎐N(4)
Si(3)᎐N(4)᎐C(17)
87.7(6)
89.8(5)
97.7(4)
89.5(5)
93.2(4)
97.1(4)
101.6(4)
76.4(2)
87.2(6)
89.8(6)
89.3(6)
177.9(7)
85.3(6)
175.9(5)
92.1(4)
119.8(7)
116.4(4)
126.2(8)
120(1)
C(1)᎐Mo(1)᎐C(3)
C(1)᎐Mo(1)᎐N(2)
C(2)᎐Mo(1)᎐C(3)
C(2)᎐Mo(1)᎐N(2)
C(3)᎐Mo(1)᎐C(4)
C(3)᎐Mo(1)᎐P(1)
C(4)᎐Mo(1)᎐P(1)
C(5)᎐Mo(2)᎐C(6)
C(5)᎐Mo(2)᎐C(8)
C(5)᎐Mo(2)᎐P(2)
C(6)᎐Mo(2)᎐C(8)
C(6)᎐Mo(2)᎐P(2)
C(7)᎐Mo(2)᎐C(9)
C(8)᎐Mo(2)᎐C(9)
C(9)᎐Mo(2)᎐P(2)
172.3(5)
87.4(4)
89.1(5)
167.8(4)
83.2(5)
89.4(4)
172.1(4)
92.3(7)
172.3(6)
95.5(4)
89.4(7)
87.5(4)
90.7(7)
88.6(7)
92.4(5)
vN ᎐H and vC᎐N at 3368m and 1578s cmϪ1, respectively. The
᎐
assignment of the NMR data is based on the chemical shifts of
2, cis-[Mo(CO)4{(Me3SiN)C(Ph)(NHPPh2)}]. The 31P-{1H}
NMR spectrum in C6D6 exhibited two singlets at δ 72.5 and
90.4 for the ᎐NPPh and the NHPPh group, respectively. In the
᎐
2
2
carbonyl region the 13C-{1H} NMR spectrum revealed five
doublets at δ 2106.5 (JP᎐CO = 8.5), 208.7 (9.8), 210.8 (23.1),
216.9 (36.5) and 220.6 (8.5 Hz) for the terminal carbonyls.
The resonances at δ 206.5 and 210.8 can be assigned to the four
carbonyls cis to and the carbonyl trans to the PPh2 group of the
Mo(CO)5 moiety, respectively. Those at δ 208.7, 216.9 and 220.6
can be assigned to the two mutually trans carbonyls, the car-
bonyl trans to the PPh2 group, and that trans to the N(SiMe3)
group of the Mo(CO)4 moiety, respectively. In addition to the
phenyl resonances, the 13C-{1H} NMR spectrum also exhibited
two doublets at δ 167.7 (JP᎐NC = 6.1) and 168.7 (18.3 Hz) for
Mo(1)᎐N(2)᎐C(10) 117.4(7)
N(1)᎐C(10)᎐N(2)
P(2)᎐N(3)᎐C(17)
Si(2)᎐N(4)᎐C(17)
Si(2)᎐N(4)᎐Si(3)
122.8(10)
135.4(9)
114.8(8)
122.4(6)
121.9(8)
the carbons of the N᎐C᎐N frameworks of the ᎐NPPh and the
᎐
2
the Mo᎐C distances of the Mo(CO)4 and Mo(CO)5 moieties
showing the expected pattern of a cis-Mo(CO)4L2 and a
Mo(CO)5L complex, respectively, with L being a poorer π acid
than CO. For the Mo(CO)4 moiety the Mo᎐C distances of the
two mutually trans-carbonyls are 2.03(1) and 2.02(1) Å for
Mo(1)᎐C(1) and Mo(1)᎐C(3), respectively, slightly longer than
the 1.94(1) and 1.95(1) Å for the carbonyls trans to the imino
N(2) and phosphino P(1) groups, respectively. For the Mo(CO)5
moiety the Mo(2)᎐C(7) distance of 2.00(1) Å for the carbonyl
NHPPh2 group, respectively, and two singlets at δ 1.4 and 4.2
for methyl carbons of the imino N(SiMe3) group and the amino
N(SiMe3)2 group, respectively. In addition to the phenyl proton
resonances the 1H NMR spectrum contains
a doublet
(JP᎐NH = 4.9 Hz) and two singlets of relative intensity 1:18:9 at
δ 5.69, 0.22 and 0.15 for the NH, N(SiMe3)2 and N(SiMe3)
protons, respectively.
A possible mechanism for the formation of compounds 1–5
is shown in Scheme 1. The compound [M(CO)4(nbd)] reacts
J. Chem. Soc., Dalton Trans., 1997, Pages 693–698
695

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Scheme 1 Possible mechanism for the formation of compounds 1–5
with the amidine to produce the intermediate I, which under-
trometer, NMR spectra on a JEOL EX270 spectrometer. Chem-
goes a rapid 1,3-silyl shift to give intermediate II. The latter is
then hydrolysed to give 1 or 2 when R = H, or to produce III
when R = C(NPPh2)[N(SiMe3)2] which reacts with [M(CO)4-
(nbd)] to give either the unsymmetric 5 or intermediate IV. The
latter then undergoes a rapid 1,3-silyl shift to give V which is
hydrolysed to give the symmetric dimer 3 or 4. A similar mech-
anism has been proposed for related complexes.5,7
ical shifts of 1H and 13C-{1H} spectra were referenced to
internal deuteriated solvents and then recalculated to SiMe4
(δ 0.00), those of 31P-{1H} spectra to external 85% H3PO4. Low-
resolution mass spectra were obtained on a Finnigan MAT
SSQ-710 spectrometer in electron-impact or FAB (positive-ion)
mode.
The iminophosphine ligand has two possible resonance
structures, C and D, as shown. Structural data for compounds
1,7 3 and 5 indicate significant delocalization about the N᎐C᎐N
framework. The contribution of the ionic resonance form D is
further supported by the fact that the imino proton of 1–5
undergoes facile deuterium exchange in D2O at ambient tem-
perature. The above data suggest that both resonance forms are
important contributors to the iminophosphine ligand.
Preparations
cis-[Cr(CO)4{(Me3SiN)C(Ph)(NHPPh2)}] 1. To a cooled
(0 ЊC) solution of (Ph2PN)C(Ph)[N(SiMe3)2] (0.42 g, 0.93
mmol) in diethyl ether (20 cm3) was added a solution of
[Cr(CO)4(nbd)] (0.24 g, 0.93 mmol) in hexane (20 cm3) dropwise
over 10 min. The resultant yellow solution was allowed to warm
to room temperature slowly and stirred for 2 d. The solvents
were removed in vacuo to give a yellow residue which was
washed with hexane (3 × 10 cm3), redissolved in diethyl ether
and filtered. The filtrate was concentrated to ca. 5 cm3 and
hexane was added to the diethyl ether solution slowly until it
just turned cloudy. The solution was then cooled to Ϫ20 ЊC to
give yellow crystals which was filtered off and dried in vacuo.
(yield: 0.38 g, 75%), m.p. 173–175 ЊC (decomp.) (Found: C,
57.9; H, 4.7; N, 5.1. Calc. for C26H25CrN2O4PSi: C, 57.8; H, 4.7;
N, 5.2%). IR (cmϪ1, in KBr): 3352s, 3056w, 2956w, 2002s,
1900vs, 1880vs, 1822s, 1606w, 1584s, 1484w, 1436m, 1408s,
1328w, 1252m, 1184w, 1156w, 1098m, 1024w, 998w, 932m, 824s,
760m, 696s, 682s, 644s, 560m and 492w. NMR (C6D6): 31P-{1H},
Experimental
Procedures
All operations were carried out in an atmosphere of dry nitro-
gen or in vacuo. Solvents were dried by standard procedures,
distilled and deaerated prior to use. All chemicals used were of
reagent grade, obtained from the Aldrich Chemical Company
and, where appropriate, degassed before use. The compounds
(Ph2PN)C(Ph)[N(SiMe3)2],3 C6H4{C(NPPh2)[N(SiMe3)2]}2-1,43
and [M(CO)4(nbd)]48 (M = Cr or Mo) were prepared according
to literature methods. Microanalyses were performed by the
Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, China. Infrared spectra (KBr pellets) were recorded
either on a Hitachi 270-30 or on a Nicolet Nagna-IR 550 spec-
δ
112,0 (s); 13C-{1H}, carbonyl carbons,
δ 220.0 (d,
JP᎐CO = 14.7), 227.7 (d, 2.5) and 228.8 (d, 13.4); C᎐N car-
bons, 169.7 (d, JP᎐NC = 19.6); phenyl carbons of CPh, 126.9,
128.9, 130.0 and 130.6; phenyl carbons of PPh2, 128.8 (d,
᎐
696
J. Chem. Soc., Dalton Trans., 1997, Pages 693–698

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cis-[{Mo(CO)4}2{(Ph2PNH)(Me3SiN3)CC6H4C(NSiMe3)-
R
C
R
(NHPPh2)}] 4. This compound was prepared as described for 3
C6H4{C(NPPh2)[N(SiMe3)2]}-1,4 (0.50 g, 0.61 mmol) and
[Mo(CO)4(nbd)] (0.37 g, 1.23 mmol) were used. Yield: 0.37 g,
55%. Yellow crystals, m.p. 168–170 ЊC (decomp.) (Found: C,
50.8; H, 3.8; N, 4.9. Calc. for C46H44Mo2N4O8P2Si2: C, 50.6; H,
4.0; N, 5.1%). IR (cmϪ1, in KBr): 3361m, 3060w, 2956w, 2023s,
1920vs, 1877vs, 1843s, 1827vs, 1582m, 1505w, 1436m, 1410s,
1248m, 1107m, 927m, 835s, 748m, 695m, 632m, 585m, 518m
and 433w. NMR (CDCl3): 31P-{1H}, PPh2, δ 89.5 (s); 13C-{1H},
carbonyl carbons, δ 207.6 (d, JP᎐CO = 9.8), 216.2 (d, 36.6) and
H
H+
C
Me3Si
Me3Si
N
N
N
N
–
PPh2
PPh2
C
D
JP᎐C = 2.4), 130.8 (d, 13.4), 137.6 (d, 4.8) and 137.7 (d,
220.5 (d, 8.6); C᎐N carbons, 167.5 (d, JP᎐NC = 18.3); phenylene
᎐
1
39.1); methyl carbons of imino N(SiMe3) group, 1.4 (s); H,
carbons, 127.6 and 130.9; phenyl carbons of PPh2, 129.9 (d,
JP᎐C = 9.8), 130.7 (d, 14.6), 137.0 (d, 37.9) and 139.8 (d,
JP᎐C = 4.9 Hz); methyl carbons of imino N(SiMe3) group, 4.1 (br,
phenyl protons, δ 7.46 (4 H, m), 7.02 (7 H, m), 6.86 (2 H, t,
J = 7.5) and 6.59 (2 H, d, J = 7.5); NH proton, δ 5.90 (1 H, d,
JP᎐NH = 6.3 Hz); protons of imino N(SiMe3) group, δ 0.17 (9 H,
s).
1
s); H, phenyl and phenylene protons, δ 7.42–7.53 (24 H, m);
NH proton, 6.15 (2 H, br, s); protons of imino N(SiMe3) group,
0.13 (18 H, br, s). Positive-ion FAB mass spectrum: m/z 1095
(M + 1 for 98Mo), 1066 (M Ϫ CO), 1038 (M Ϫ 2CO), 1010
(M Ϫ 3CO), 982 (M Ϫ 4CO), 954 (M Ϫ 5CO), 926 (M Ϫ
6CO), 898 (M Ϫ 7CO) and 870 (M Ϫ 8CO).
cis-[Mo(CO)4{(Me3SiN)C(Ph)(NHPPh2)}] 2. This com-
pound was prepared as described for 1: [Mo(CO)4(nbd)] (0.32 g,
1.06 mmol) and (Ph2PN)C(Ph)[N(SiMe3)2] (0.48 g, 1.06 mmol)
were used. Yield: 0.45 g, 70%. Yellow crystals, m.p. 132–134 ЊC
(decomp.) (Found: C, 51.7; H, 4.4; N, 4.3. Calc. for
C26H25MoN2O4PSiؒH2O: C, 51.8; H, 4.5; N, 4.7%). IR (cmϪ1, in
KBr): 3356s, 3056w, 2956w, 2012s, 1908vs, 1876vs, 1834s,
1604w, 1582s, 1482w, 1414s, 1250m, 1182w, 1156w, 1128w,
1094m, 1024w, 998w, 930m, 842s, 828s, 740m, 694s, 622m, 584s,
560m and 506w. NMR (C6D6): 31P-{1H}, δ 89.6 (s); 13C-{1H},
carbonyl carbons, δ 208.7 (d, JP᎐CO = 9.8), 217.0 (d, 36.6) and
cis-[(OC)4Mo{Ph2PNH)(Me3SiN3)CC6H4C[N(SiMe3)2]-
(NPPh2)}Mo(CO)5] 5. This compound was prepared as
described for 1: [Mo(CO)4(nbd)] (0.49 g, 1.60 mmol) and
C6H4{C(NPPh2)[N(SiMe3)2]}2-1,4 (0.67 g, 0.80 mmol) were
used. Yield: 0.58 g, 60%. Yellow crystals, m.p. 144–146 ЊC
(decomp.) (Found: C, 49.7; H, 4.5; N, 4.3. Calc. for
C50H52Mo2N4O9P2Si3ؒH2O: C, 49.7; H, 4.5; N, 4.6%). IR (cmϪ1
,
220.7 (d, 8.5); C᎐N carbons, 169.9 (d, JP᎐NC = 18.2); phenyl
᎐
in KBr): 3368m, 3060w, 2956w, 2068m, 2016m, 1940s (br),
1908vs, 1878s, 1830s, 1578s, 1432w, 1406m, 1252s, 1180w,
1136m, 1092m, 964w, 926w, 828s, 686m, 580m and 520m.
carbons of CPh, 127.0, 129.6, 130.2 and 130.9; phenyl carbons
of PPh2, 129.1 (d, JP᎐C = 8.5), 131.2 (d, 15.9), 138.0 (d, J 39.0)
and 138.1 (d, 4.9); methyl carbons of imino N(SiMe3) group,
1.6 (s); 1H, phenyl protons, δ 7.41 (4 H, m), 7.00 (2 H, m), 6.83
(2 H, t, J = 7.3) and 6.60 (2 H, d, J = 7.3); NH proton, 5.79 (1 H,
d, JP᎐NH = 4.6 Hz); protons of imino N(SiMe3) group, 0.15 (9 H,
s); and H2O protons, 0.29 (2 H, s). Electron impact mass spec-
trum: m/z: 586 (M for 98Mo), 558 (M Ϫ CO), 530 (M Ϫ 2CO),
502 (M Ϫ 3CO) and 474 (M Ϫ 4CO).
NMR (C6D6): 31P-{1H}, ᎐NPPh , δ 72.5 (s); HNPPh , 90.4 (s);
᎐
2
2
13C-{1H}, carbonyl carbons, 206.5 (d, JP᎐CO = 8.5), 208.7 (d,
9.8), 210.8 (d, 23.1), 216.9 (d, 36.5) and 220.6 (d, 8.5); C᎐N
᎐
carbons, 167.7 (d, JP᎐NC = 6.1) and 168.7 (d, 18.3); phenyl and
phenylene carbons, 126.4 (s), 128.8–132.1 (m), 137.3 (s), 137.9
(s), 138.6 (d, JP᎐C = 4.9) and 141.5 (d, 3.7); methyl carbons of
imino N(SiMe3) group, 1.4 (s); methyl carbons of the amino
N(SiMe3)2 group, δ 4.2 (s); 1H, phenyl and phenylene protons, δ
7.70, (4 H, m), 7.38 (7 H, m), 7.10 (8 H, m), 6.79 (4 H, m), 6.59 (2
H, m) and 6.45 (2 H, d, J = 8.4); NH proton, 5.69 (1 H, d,
JP᎐NH = 4.9 Hz); protons of amino N(SiMe3)2 group, 0.22 (18 H,
s); protons of imino N(SiMe3) group, 0.15 (9 H, s); H2O pro-
tons, 0.29 (2 H, s).
cis-[{Cr(CO)4}2{(Ph2PNH)(Me3SiN)CC6H4C(NSiMe3)-
(NHPPh2)}], 3. To a cooled (Ϫ78 ЊC) solution of C6H4-
{C(NPPh2)[N(SiMe3)2]}2-1,4 (0.50 g, 0.61 mmol) in tetrahydro-
furan (30 cm3) was added to a solution of [Cr(CO)4(nbd)] (0.31
g, 122 mmol) in tetrahydrofuran (10 cm3) dropwise over 10 min.
The resultant orange solution was allowed to warm to room
temperature slowly and stirred for 2 d. It was concentrated to
ca. 10 cm3 and hexane (30 cm3) added to afford a yellow solid.
The solid was filtered off, washed with diethyl ether (3 × 2 cm3),
dissolved in CH2Cl2 (5 cm3) and filtered. Hexane was added to
the CH2Cl2 solution slowly until it just turned cloudy. It was
then cooled to Ϫ20 ЊC to give yellow crystals which were fil-
tered off and dried in vacuo. (yield: 0.33 g, 50%), m.p. 126–
128 ЊC (decomp.) (Found: C, 49.6; H, 4.3; H, 4.9. Calc. for
C46H44Cr2N4O8P2Si2ؒ2CH2Cl2: C, 49.2; H, 4.1; N, 4.8%). IR
(cmϪ1, in KBr): 3348w, 3200w, 3060w, 2959w, 2012s, 1898vs,
1884vs (sh), 1840vs, 1578m, 1414m, 1252m, 1105m, 937m,
843m, 698m, 649s, 527w and 501w. NMR (C6D6): 31P-{1H},
PPh2: δ 112.3 (br, s); 13C-{1H}, carbonyl carbons, δ 219.9 (d,
X-Ray crystallography
Crystals of compound 3 suitable for X-ray diffraction study
were grown by slow diffusion of diethyl ether into a saturated
solution of the compound 3 in CH2Cl2 as a solvate of stoichio-
metry 3ؒ2CH2Cl2. A yellow block of dimensions 0.20 ×
0.38 × 0.45 mm was mounted on a glass fibre with epoxy resin.
Intensity data were collected on a Siemens P4 diffractometer at
294
K
with graphite-monochromated Mo-Kα radiation
(λ = 0.710 73 Å) using ω–2θ scans. Crystal stability was moni-
tored by recording three check reflections at intervals of 97 data
measurements, and no significant variation was detected. An
empirical absorption correction based on ψ scans was applied,
resulting in relative transmission factors ranging from 0.8751 to
0.9485. A total of 5110 unique reflections (3 р 2θ р 50Њ) were
measured; 2637 of these had I > 2.0σ(I) and were considered
observed. Crystal data, data collection parameters, and results
of the analysis are given in Table 3. The structure was solved by
the direct method using the program package SHELXTL
PLUS9 and refined against F 2 using SHELXL 93.10 Non-
hydrogen atoms were refined anisotropically by full-matrix least
squares. The SiMe3 group and the CH2Cl2 solvent molecules
were positionally disordered. The atomic positional and thermal
parameters of the carbon atoms of the SiMe3 group and the
JP᎐CO = 14.6), 227.3 (br, s) and 228.5 (d, J 13.4); C᎐N carbons,
᎐
167.9 (d, JP᎐NC = 26.7); phenylene carbons, 127.6 and 130.9;
phenyl carbons of PPh2, 129.90 (d, JP᎐C = 9.8), 130.7 (d, 13.4),
137.5 (d, 39.0) and 139.4 (d, J 6.1 Hz); methyl carbons of
imino N(SiMe3) group, 4.3 (br, s); 1H, phenyl protons, δ 7.51 (8
H, m) and 7.01 (12 H, m); phenylene protons, 6.55 (2 H, s) and
4.25 (2 H, s); NH proton, 6.02 (2 H, br, s); protons of imino
N(SiMe3) group, 0.24 (18 H, br, s). Positive-ion FAB mass spec-
trum: m/z: 1003 (M + 1), 918 (M Ϫ 3CO), 890 (M Ϫ 4CO), 862
(M Ϫ 5CO), 834 (M Ϫ 6CO), 806 (M Ϫ 7CO) and 778
(M Ϫ 8CO).
J. Chem. Soc., Dalton Trans., 1997, Pages 693–698
697

View Article Online
were considered observed. The data were corrected for Lorentz-
polarization factors and absorption using the ψ-scan method.
The structure was solved by direct methods and refined by full-
matrix least-squares analysis, with all non-hydrogen atoms
assigned anisotropic displacement parameters. Half-occupancy
was assigned to the carbons of the disordered hexane solvent
molecule which were restrained during refinement. Hydrogen
atoms were treated as in 3. All calculations were performed on a
Silicon-Graphics computer using the program package TEX-
SAN.11 The relatively high R values are due to poor crystal
quality and severe positional disorder of the hexane molecule.
Atomic coordinates, thermal parameters and bond lengths
and angles, have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue. 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/338.
Table 3 Data collection and processing parameters for compounds 3
and 5*
3
5
Empirical formula
C48H48Cl4Cr2N4O8-
P2Si2
C53H59Mo2N4O9-
P2Si3
M
1172.8
1.348
1234.1
1.290
Dc/g cmϪ3
Crystal size/mm
Space group
0.20 × 0.38 × 0.45
I2/a (no. 15,
non-standard)
17.337(3)
15.055(3)
22.652(4)
102.22(1)
5778(2)
0.32 × 0.33 × 0.36
P21/n (no. 14,
non-standard)
16.080(3)
17.933(3)
23.105(3)
107.67(1)
6348(1)
a/Å
b/Å
c/Å
β/Њ
U/Å3
µ/cmϪ1
7.08
5.51
F(000)
2400
2528
Scan rate/Њ minϪ1 in ω
Variable, 6.00–60.00 16.0 (up to 4
scans)
Acknowledgements
Scan range (ω)
Reflections collected
Independent reflections
(0.60 + 0.35 tan θ)Њ
5230
5110 (0.0335)
(1.68 + 0.35 tan θ)Њ
8981
8622 (0.041)
W.-K. Wong thanks the Hong Kong Baptist University and the
Hong Kong Research Grants Council for financial support.
W.-T. Wong thanks the Hong Kong Research Grants Council
and the University of Hong Kong for financial support.
(Rint
)
Observed reflections
Quantity minimized
Weighting scheme, wϪ1
R, RЈ (observed data)
Goodness of fit
2637 [Io > 2.0 σ(Io)] 5230 [Io > 1.5 σ(Io)]
2
Σw(Fo2 Ϫ Fc )2
σ2(Fo) + 0.0005Fo
0.063, 0.065
1.32
Σw(Fo Ϫ Fc)2
σ2(Fo)
0.065, 0.068
3.33
2
References
Largest ∆/σ
0.009
0.09
1 J. A. Dodge, I. Manners, H. R. Allcock, G. Renner and O. Nuyken,
J. Am. Chem. Soc., 1990, 112, 1268 and refs. therein.
2 V. Chandrasekhar, T. Chivers, S. S. Kumaravel, A. Meetsma and
J. C. van de Grampel, Inorg. Chem., 1991, 30, 3402 and refs. therein.
3 T. Chivers, K. McGregor and M. Parvez, Inorg. Chem., 1993, 32,
5119.
4 W. K. Wong, T. Jiang and W. T. Wong, J. Chem. Soc., Dalton Trans.,
1995, 3087.
5 W. K. Wong, T. Jiang, D. W. J. Kwong and W. T. Wong, Polyhedron,
1995, 14, 1109.
6 K. R. Dixon, Multinuclear NMR, ed. J. Mason, Plenum, New York,
1987, ch.13.
7 W. K. Wong, T. Jiang, D. W. J. Kwong and W. T. Wong, Polyhedron,
1995, 14, 1695.
8 J. J. Eisch and R. B. King, Organometallic Synthesis, Academic
Press, New York, 1965, vol. 1, pp. 124–125.
9 G. M. Sheldrick, Computational Crystallography, ed D. Sayre,
Oxford University Press, New York, 1982, p. 506, Crystallographic
Computing 3, eds. G. M. Sheldrick, C. Kruger and R. Goddard,
Oxford University Press, New York, 1985, p. 175.
10 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure
Refinement, University of Göttingen, 1993; Crystallographic Com-
puting 6: A Window on Modern Crystallography, eds. H. D. Flack,
L. Párkányi and K. Simon, Oxford University Press, New York,
1993.
Number of parameters, p 376
631
0.84 to Ϫ0.48
Residual extrema/e ÅϪ3
0.36 to Ϫ0.43
* Details in common: yellow block; monoclinic; Z = 4.
non-hydrogen atoms of the CH2Cl2 solvent molecules were
refined with occupancy 0.5. Hydrogen atoms were generated in
their idealized positions (C᎐H 0.95 and N᎐H 0.85 Å) and
allowed to ride on their respective parent carbon and nitrogen
atoms. These hydrogen atoms were assigned appropriate iso-
tropic thermal parameters and included in the structure-factor
calculations but not in the refinement. The relatively high R
values are due to poor crystal quality, thermal disorder of the
SiMe3 groups, and severe positional disorder of the CH2Cl2
molecules.
Crystals of compound 5 suitable for X-ray diffraction study
were grown by slow diffusion of hexane into a saturated solu-
tion of it in CH2Cl2 as a solvate of stoichiometry 5ؒ0.5C6H14.
A yellow block of dimensions 0.32 × 0.33 × 0.36 mm was
mounted on a glass fibre with epoxy resin. Intensity data were
collected on a Rigaku AFC7R diffractometer at 298 K with
graphite-monochromated. Mo-Kα radiation using ω–2θ scans.
Crystal stability was monitored by recording three check reflec-
tions at intervals of 150 data measurements, and no significant
variation was detected. A total of 8622 unique reflections
(6 р 2θ р 45Њ) were measured; 5230 of these had I > 1.5σ(I) and
11 TEXSAN, Crystal Structure Analysis Package, Molecular Structure
Corporation, Houston, TX, 1985 and 1992.
Received 29th October 1996; Paper 6/07373E
698
J. Chem. Soc., Dalton Trans., 1997, Pages 693–698