Synthesis, redox chemistry, and electronic structure of the alkynyl cyclopentadienyl molybdenum complexes [Mo(C≡CR)(CO)(L2)Cp] n+ (n = 0 or 1; R = Ph or C6H4-4-Me, L 2 = Ph2PCH2C

ARTICLE

pubs.acs.org/Organometallics

Synthesis, Redox Chemistry, and Electronic Structure of the Alkynyl

Cyclopentadienyl Molybdenum Complexes [Mo(CtCR)(CO)(L₂)Cp⁰]ⁿ⁺

(n = 0 or 1; R = Ph or C₆H₄-4-Me, L₂= Ph₂PCH₂CH₂PPh₂or 2PMe₃,

Cp⁰= Cp or Cp*)

Hannah N. Roberts (nꢀee Lancashire),^†Neil J. Brown,^‡Ruth Edge,^§Ross Lewin,^†David Collison,*^,§

Paul J. Low,*^,‡and Mark W. Whiteley*^,†

^†School of Chemistry, University of Manchester, Manchester, M13 9PL, U.K.

^‡Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, U.K.

^§EPSRC National Service for EPR Spectroscopy, School of Chemistry, University of Manchester, Manchester, M13 9PL, U.K.

S Supporting Information

b

ABSTRACT: Two series of bis-phosphine-substituted cyclopentadienyl

molybdenum alkynyl complexes, [Mo(CtCR)(CO)(dppe)Cp⁰] and

trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰] (R = Ph or C₆H₄-4-Me, dppe =

Ph₂PCH₂CH₂PPh₂, Cp⁰= Cp or Cp*), have been prepared and structurally

characterized. One-electron oxidation to the 17-electron radical cations has

been investigated by cyclic voltammetry and, for selected Cp* derivatives, by

spectroelectrochemical IR and UVꢀvisible methods. Through a combination

of experimental measurements (IR and EPR spectroscopy) and DFT-based

calculations some important diﬀerences between the two series of complexes

[Mo(CtCR)(CO)(dppe)Cp⁰] and trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰] have been established. In particular, the change in

molecular geometry leads to enhanced alkynyl character in the HOMO of [Mo(CtCR)(CO)(dppe)Cp⁰] when compared with the

largely metal-centered HOMO of trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰].

’ INTRODUCTION

that of related complexes of the Fe, Ru, and Re systems. Thus the

increase in ring size from Cp to C₇H₇promotes strong metalꢀ

ring δ-interactions, leading to a reordering of the metal d-orbital

manifold and a HOMO with substantial metal d_z₂character. This

in turn results in a reduced interaction between the metal and the

alkynyl π-orbitals.^7a

The chemistry of carbon chain ligands attached to redox-

active, half-sandwich metal support groups is the focus of

intense current research activity. A series of monometallic¹[M-

(CtC)_nR] and ligand-bridged bimetallic²[M-(CtC)_n-M]

complexes has been investigated, notably for the electron-rich

d⁶metal centers, M = Fe(dppe)Cp*,³Ru(P₂)Cp⁰(P₂= 2PPh₃,

Cp⁰= Cp;⁴P₂= dppe, Cp⁰= Cp*⁵), Re(NO)(PPh₃)Cp*,⁶and

Mo(dppe)(η-C₇H₇),⁷which confer enhanced stability to the

products of oxidative redox chemistry. Each of these half-

sandwich metal support groups imparts a distinctive character

to the redox chemistry of their carbon chain complexes, and this

can be attributed, in part, to their electronic structure and the

composition of the redox orbital. For example, alkynyl derivatives

of Ru(P₂)Cp⁰and Re(NO)(PPh₃)Cp* systems feature HOMOs

with signiﬁcant carbon chain contribution derived from good

overlap between metal 4d/5d orbitals and the ﬁlled π-orbitals of

the CtC bond. By contrast, the metal auxiliaries Fe(dppe)Cp*

and Mo(dppe)(η-C₇H₇) possess HOMOs which are substan-

tially more metal localized. In the case of Fe(dppe)Cp* this has

been rationalized by the reduced overlap of the 3d-orbitals of a

ﬁrst-row metal with the carbon chain ligand π-system. However

the metal-centered character of the HOMO of the cyclohepta-

trienyl-molybdenum complex [Mo(CtCR)(dppe)(η-C₇H₇)]

arises from a fundamental diﬀerence in electronic structure to

These observations suggested that an understanding of the

correlation between electronic structure and the redox chemistry

of carbon chain complexes could be applied to the ﬁne-tuning of

key properties of half-sandwich alkynyl complexes, including

reactivity at the carbon chain and spin density distribution, via

alteration of variables such as ring size, d-transition series, and the

molecular geometry at the metal center. To explore this concept

further, we have initiated a series of investigations into the

electronic structure and redox chemistry of an extended set of

electron-rich, half-sandwich, metal alkynyl complexes.⁸This

report describes the synthesis, redox chemistry, and electronic

structures of the cyclopentadienyl molybdenum alkynyl com-

plexes [Mo(CtCR)(CO)(L₂)Cp⁰] (R = Ph, C₆H₄-4-Me; L₂=

dppe or 2PMe₃, Cp⁰= Cp or Cp*). These complexes provide the

opportunity to assess the eﬀect of molecular geometry with the

“four-leg piano stool” conﬁguration, representing a departure

Received: March 15, 2011

Published: June 28, 2011

r

2011 American Chemical Society

3763

dx.doi.org/10.1021/om200229c Organometallics 2011, 30, 3763–3778

|

Organometallics

ARTICLE

Table 1. Compound Numbering Scheme for

Scheme 1. Synthetic Routes to [Mo(CtCR)(CO)(L₂)Cp]

[MoX(CO)(L₂)Cp⁰] and [Mo(CtCR)(CO)(L₂)Cp⁰]

Complexes^a

complex

X/CtCR

L₂

Cp⁰

1a

1b

2a

3a

4b

5a

5b

6a

6b

7a

7b

8a

8b

9b

Cl

Br

Cl

dppe

Cp

Cp*

Cp

2PPh₃

Cp

2PMe₃

dppe

Cp*

Cp

CtCPh

dppe

Cp*

Cp

CtCC₆H₄-4-Me

CtCPh

dppe

Cp*

Cp

(CO)(PMe₃)

2PMe₃

CtCPh

Cp*

Cp

CtCPh

Cp*

CtCC₆H₄-4-Me

from previous studies. Moreover the location of the alkynyl ligand

trans to a P-donor or CO ligand in [Mo(CtCR)(CO)(dppe)Cp⁰]

and trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰], respectively, presents a

further possibility for the control of electronic structure and redox

properties by variation of coordination geometry. Finally the combi-

nation of CO and CtCR ligands in these complexes provides a dual

IR spectroscopic probe for monitoring changes in electron density at

the metal and alkynyl ligand resulting from variation in redox state.

^aReagents and conditions (i) (a) HCtCR/MeOH reﬂux, (b) CO gas;

(ii) NaOMe or KOBu^tin MeOH; (iii) PMe₃, Me₃NO in CH₃CN

(1ꢀ2 h.); (iv) PMe₃in toluene, UV (3 h).

protocol for the synthesis of alkynyl complexes at a d⁶metal

center such as Ru(PPh₃)₂Cp or Mo(dppe)(η-C₇H₇).^4,7aIn the

current investigation, the Mo(CO)(L₂)Cp⁰unit is formally

Mo(II), d⁴, and, as well-documented, the lower d-electron count

leads to a reduced preference for the intermediate vinylidene

complex [Mo(CdCHR)(CO)(L₂)Cp⁰]⁺versus the decarbonylated

four-electron alkyne product [Mo(HCtCR)(L₂)Cp⁰]⁺.^14,15How-

ever, as reported previously by Lin et al.,¹⁶reaction of [MoCl-

(CO)(dppe)Cp], 1a, with HCtCPh in reﬂuxing MeOH, followed

by sequential treatment with CO and NaOMe, can aﬀord [Mo-

(CtCPh)(CO)(dppe)Cp], 5a, via the intermediate η²-alkyne and

η¹- vinylidene complexes [Mo(HCtCPh)(dppe)Cp]Cl and [Mo-

(CdCHPh)(CO)(dppe)Cp]Cl. This method was extended to the

preparation of the new derivatives [Mo(CtCC₆H₄-4-Me)(CO)-

(dppe)Cp], 6a, and the pentamethylcyclopentadienyl analogues

[Mo(CtCR)(CO)(dppe)Cp*] (R = Ph, 5b, R = C₆H₄-4-Me,

6b), demonstrating ﬂexibility of the synthetic route in terms of

alkynyl substituent and substitution at the cyclopentadienyl ring.

The intermediate Cp* vinylidene complexes [Mo(CdCHR)(CO)

(dppe)Cp*]⁺exhibited enhanced stability with respect to loss of CO,

but the syntheses of the Cp* alkynyls 5b and 6b were still best con-

ducted including CO as a reagent.

Attempts to eﬀect an analogous synthesis of trans-phosphine

alkynyl complexes commencing from trans-[MoCl(CO)(PPh₃)₂-

Cp], 3a, or trans-[MoCl(CO)(PMe₃)₂Cp*], 4b, were unsuccess-

ful; however an alternative route starting from [Mo(CtCR)-

(CO)₃Cp⁰] (R = Ph or C₆H₄-4-Me) involving stepwise substitu-

tion of CO by PMe₃was productive. In the ﬁrst step, Me₃NO-

assisted decarbonylation of [Mo(CtCR)(CO)₃Cp⁰] in NCMe¹⁷

in the presence of PMe₃aﬀorded the monosubstituted

derivatives [Mo(CtCR)(CO)₂(PMe₃)Cp⁰] (isolated and fully

characterized for the examples R = Ph, Cp⁰= Cp, 7a; Cp⁰= Cp*,

7b). Subsequent photolysis of [Mo(CtCR)(CO)₂(PMe₃)Cp⁰]

with excess PMe₃in toluene resulted in partial conversion to

’ RESULTS AND DISCUSSION

Synthetic Studies. A series of precursor halide derivatives

[MoX(CO)(L₂)Cp⁰] and the alkynyl complexes [Mo(CtCR)

(CO)(L₂)Cp⁰] were synthesized starting from [MoX(CO)₃Cp⁰];

a summary of the systems investigated is presented in Table 1.

Each of the halide complexes (1a, 1b, 2a, 3a, 4b) was obtained

by direct reaction of [MoX(CO)₃Cp⁰] with the selected phos-

phine ligand in reﬂuxing toluene and puriﬁed by column

chromatography on alumina to give the products as orange or

yellow solids in moderate yield. All are known complexes,^9ꢀ13

but a direct thermal substitution method has not been previously

employed for the Cp* derivatives 1b and 4b. Replacement of Cp

by Cp* (complexes 1b and 4b) resulted in increased reaction

times, but the syntheses still proceeded cleanly; in fact, the

additional stability conferred by the Cp* ligand is advantageous

to the synthesis of 4b since attempts to obtain trans-[MoCl-

(CO)(PMe₃)₂Cp] by direct reaction of [MoCl(CO)₃Cp] with

PMe₃led to partial decomposition. Selected characterization

details (microanalysis, IR, mass, ¹H and ³¹P NMR spectroscopy),

suﬃcient to establish the identity and purity of the materials

obtained by the direct carbonyl substitution route, are given in

the Experimental Section. The diﬀerent molecular geometry of

the two series of complexes, the cis-phosphine, dppe complexes

1a, 1b, and 2a, and the trans-phosphine, PPh₃and PMe₃systems

3a and 4b, is evident from the number of phosphorus environ-

ments in the ³¹P{¹H} NMR spectra (see Experimental Section).

The successful synthetic routes to the bis-phosphine-substi-

tuted alkynyl complexes, as dppe derivatives, 5a, 5b, 6a, and 6b,

and trans-PMe₃complexes 8a, 8b, and 9b are summarized in

Scheme 1. Isomerization of a terminal alkyne to a coordinated

vinylidene followed by deprotonation is a well-established

3764

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Table 2. C{¹H} NMR Data for [Mo(CtCR)(CO)(L₂)Cp⁰]^a

13

C_R

C_β

CO

Cp⁰(Cp or Cp*)

L/L₂= dppe or PMe₃

R

b

5a 119.8, d,

br, J(PꢀC) ca. 47

5b 135.2, d, br,

J(PꢀC) ca. 53

6a 117.1, dd,

J(PꢀC), 49, 3.9

6b not observed

123.6

245.2, d,

J(PꢀC) 22.1

246.1, d,

J(PꢀC) 19.1

245.2, d,

J(PꢀC) 22.1

245.9, d,

J(PꢀC) 20.1

252.9, d,

J(PꢀC) 31.2; 238.1, br

126.3, br 256.4, d,

J(PꢀC) 0.2; 241.5, br

124.5, br 259.0, t,

J(PꢀC) 30.5

126.0, br 267.2, t,

J(PꢀC) 33.2

125.6, br 267.6, t,

91.1

141.8ꢀ127.2, PPh₂;

31.8, m, CH₂; 28.6, m, CH₂

138.5ꢀ127.5, PPh₂;

123.1

126.1

121.6

126.9

101.5, 10.7

91.0

31.0, m, CH₂; 27.0, m, CH₂

141.9ꢀ127.6, PPh₂;

31.7, m, CH₂; 28.7, m, CH₂

138.7ꢀ126.9, PPh₂; 31.1,

m, CH₂; 27.0, m, CH₂

19.7, d, J(PꢀC) 33.2

21.8, C₆H₄-Me-4^b

21.1, C₆H₄Me-4^b

101.4, 10.7

91.8

7a 109.6, d,

J(PꢀC) 48.3

7b 120.8, d,

J(PꢀC) 7.3

8a 129.7, t,

J(PꢀC) 47.8

8b 137.0, t,

J(PꢀC) 49.2

9b 134.8, t,

130.3, d, J(PꢀC) 3, C_o/m; 128.0, C_i/o/m

;

125.1, C_p

104.2, 11.2

88.7

18.0, d, J(PꢀC) 30.2

18.8, m

130.1, d, J(PꢀC) 2, C_o/m; 128.8, d,

J(PꢀC) 3, C_i; 128.0, s, C_o/m; 124.7, C_p

128.6, m, C_o/m; 128.0, br, C_i; 127.0, C_o/m

;

123.0, C_p

100.6, 10.8

17.7, m

128.4, br, C_i; 128.3, m, C_o/m; 127.0, C_o/m

122.7, C_p

;

17.7, m

138.5, C_p, 128.9, C_i; 128.1, 127.8 C_o/m; 21.3,

J(PꢀC) 49.8

J(PꢀC) 33.2

C₆H₄Me-4

^a100 MHz spectra; s = singlet, d = doublet, t = triplet, m = multiplet, br = broad; chemical shifts downﬁeld from SiMe₄, coupling constants in Hz. In

CDCl₃solution unless stated otherwise. ^bAssignment of aryl carbons of the alkynyl substituent R impeded by overlap with dppe Ph carbons.

the required bis-substituted complexes trans-[Mo(CtCR)(CO)-

(PMe₃)₂Cp⁰] (R = Ph, Cp⁰= Cp, 8a; Cp⁰= Cp*, 8b; R = C₆H₄-4-

Me, Cp⁰= Cp*, 9b), which were separated from their precursors by

chromatography on alumina and isolated as yellow-orange solids.

With the exception of [Mo(CtCPh)(CO)(dppe)Cp], 5a, the

alkynyl complexes presented in this work have not been reported

previously, although analogues of 7a and 8a (notably trans-[Mo-

(CtCBu^t)(CO)(PMe₂Ph)₂Cp])¹⁴are known. The phosphine-

substituted derivatives of the Cp* system, i.e., 5b, 6b, 7b, 8b, and 9b,

appear to be the ﬁrst examples of complexes of this type.

The ν(CtC) band in the IR spectra of the dppe derivatives 5a/b

and 6a/b lies in a narrow range around 2070 cm^ꢀ1, toward the high

end of values observed for [M(CtCR)(dppe)(η-L)] (R = Ph,

C₆H₄-4-Me; M = Fe or Ru, L = Cp, Cp*; M = Mo, L = C₇H₇).^4,6,7

However, complexes trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰] (8a/b

and 9b), in which the alkynyl ligand is positioned trans to the strongly

π-accepting CO ligand, exhibit ν(CtC) approximately 20 cm^ꢀ1

lower than the analogous dppe systems where the alkynyl ligand is

arranged trans to a P-donor atom. An additional IR spectroscopic

handle in complexes of the type [Mo(CtCR)(CO)(L₂)Cp⁰], not

available to related investigations on the systems [M(CtCR)

(dppe)(η-L)] (M = Fe or Ru, L = Cp, Cp*; M = Mo, L = C₇H₇),

is the carbonyl ν(CO) band. The principal factor governing ν(CO) is

the cis versus trans geometry of the complex with trans-phosphine

complexes exhibiting ν(CO) signiﬁcantly lower (60ꢀ70 cm^ꢀ1) than

analogous dppe derivatives. This feature is also evident for halide

analogues (cf. [MoCl(CO)(dppe)Cp], 1a, and trans-[MoCl(CO)-

(PPh₃)₂Cp], 3a;ν(CO), (CH₂Cl₂):1a, 1847 cm^ꢀ1;3a, 1792cm^ꢀ1)

and probably reﬂects the strong π-donor capacity of both halide and

alkynyl ligands positioned trans to the carbonyl. In fact for any two

related complexes [MoX⁰(CO)(L₂)Cp⁰] (X⁰= Cl or CtCR), the

change in ν(CO) on substitution of Cl by CtCR is not more than a

few wavenumbers. This π-donor halide to π-acceptor carbonyl

interaction may strengthen the MoꢀCl bond in complexes 3a and

4b and account for their lack of reactivity toward terminal alkynes.

Finally, ν(CO) is sensitive to substitution of Cp by Cp* with a shift of

approximately 20 cm^ꢀ1to lower wavenumber in all Cp* derivatives.

Structural Investigations. The X-ray crystal structures of the

bis-phosphine alkynyl complexes 5b, 6a, 6b, 8a, 8b, and 9b have

been determined, and important bond lengths and angles are

summarized in Table 3. Representative structures, 6a, 6b, 8a, and

8b, are shown in Figures 1 to 4, respectively, together with details

of the structure of the monophosphine derivative 7b (Figure 5).

In the series of complexes 5b, 6a/b, 8a/b, and 9b, the MoꢀC_R

bond length lies in the approximate range 2.12ꢀ2.14 Å, con-

sistent with typical values for 18-electron molybdenum alkynyl

The alkynyl complexes 5a/b, 6a/b, 7a/b, 8a/b, and 9b were

characterized by microanalysis, mass spectrometry, infrared

spectroscopy, and by ¹H, ³¹P{¹H}, and ¹³C{¹H} NMR spectros-

copy (see Experimental Section and Table 2). Parameters

diagnostic of the presence of the alkynyl ligand in these systems

are the C_Rresonance in the ¹³C{¹H} NMR spectrum and the IR-

active ν(CtC) band. In the case of the cyclopentadienyl dppe

complexes [Mo(CtCR)(CO)(dppe)Cp] (5a and 6a), δ C_Ris

located in the range 117ꢀ120 ppm; for 6a, a resolved doublet of

doublets pattern [J(PꢀC) ≈ 50, 4 Hz] was observed for C_R,

consistent with coupling to two inequivalent phosphorus envi-

ronments. In the Cp* derivative [Mo(CtCPh)(CO)(dppe)

Cp*], 5b, C_Ris shifted to low ﬁeld by comparison with 5a and

is observed at δ 135.2 as a broad doublet with J(PꢀC_R) ≈ 53 Hz.

For [Mo(CtCC₆H₄-4-Me)(CO)(dppe)Cp*], 6b, a shift in C_R

to high ﬁeld by ca. 2 ppm is expected, resulting from the more

strongly donating alkynyl substituent, and attempts to locate C_R

were unsuccessful, probably as a consequence of overlap of the

C_Rresonance with the C_o/mcarbons of the dppe Ph groups. A

doublet resonance was also observed for C_Rin the monophosphine

complexes [Mo(CtCPh)(CO)₂(PMe₃)Cp⁰], 7a/b, and the detec-

tion of two discrete resonances for the carbonyl carbons establishes a

cis-carbonyl geometry.^17,18In the trans bis-phosphine complexes

trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰], 8a/b and 9b, C_Ris observed

as a triplet around 130ꢀ135 ppm with a J(PꢀC) coupling of ca. 50 Hz

to the two equivalent phosphorus atoms.

3765

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Table 3. Key Bond Lengths (Å) and Angles (deg) for [Mo(C_rtC_βR)(CO)(L₂)Cp⁰]

5b

6a

6b

8a

2.129(6)

8b

9b

MoꢀC_R

Mo-CO

2.120(3)

1.899(3)

1.186(3)

2.4756(7)

2.4755(7)

1.216(3)

1.431(4)

2.135(9)

1.97(1)

1.15(1)

2.429(2)

2.467(2)

1.21(1)

1.43(1)

2.113(4)

1.920(4)

1.175(4)

2.460(1)

2.468(1)

1.210(5)

1.441(5)

2.118(3)

1.909(3)

1.183(3)

2.118(2)

1.937(2)

1.171(3)

1.923(6)

CtO

1.168(7)

MoꢀP_cis

2.423(2) 2.426(2)

2.4347(7) 2.4413(8)

2.4150(6) 2.4381(6)

MoꢀP_trans

C_RꢀC_β

1.221(9)

1.217(3)

1.215(3)

C_βꢀC_{(substituent)}

P_cisꢀMoꢀP_cis

C_RꢀMoꢀ P_cis

C_RꢀMoꢀP_trans

C_RꢀMoꢀCO

P_cisꢀMoꢀCO

P_transꢀMoꢀCO

MoꢀC_RꢀC_β

C_RꢀC_βꢀC_{(substituent)}

1.432(8)

1.442(4)

1.433(3)

123.24(6)

74.2(2) 73.6(2)

116.97(3)

113.79(2)

73.35(7)

140.91(7)

80.6(1)

72.9(2)

136.0(2)

78.7(3)

108.0(3)

80.5(3)

173.8(7)

175.9(9)

71.2(1)

134.8(1)

78.5(1)

104.4(1)

80.0(1)

175.3(3)

175.2(4)

72.09(7) 73.65(7)

74.05(6) 73.06(6)

115.0(2)

117.9(1)

121.61(9)

97.60(8)

81.74(8)

173.2(2)

176.0(3)

77.0(2), 76.1(2)

75.98(8) 75.82(8)

75.72(7) 75.39(7)

175.2(5)

176.4(7)

176.9(2)

175.3(3)

173.4(2)

176.6(2)

Figure 1. Plot of the molecular structure of 6a showing the atom-

labeling scheme. In this and all subsequent structural ﬁgures, thermal

ellipsoids are plotted at 50% probability. Hydrogen atoms have been

omitted for clarity.

Figure 2. Plot of the molecular structure of 6b showing the atom-

labeling scheme.

together with the related chloride complexes [MoCl(CO)(dppe)-

Cp], 1a,²¹and trans-[MoCl(CO)(PMe₂Ph)₂Cp*], 4b⁰,²⁴are

summarized in Table 4.

complexes ([Mo(CtCPh)(dppe)(η-C₇H₇)], 2.138(5) Å,^7a

[MoH₃(CtCBu^t)(dppe)₂], 2.175(10) Å,¹⁹and [Mo(CtCPrⁿ)

(CO)₂(dppe)(NO)], 2.182(4) Å²⁰). The MoꢀP distances also

lie within normal ranges, although the trend of elongation of

MoꢀP_ciswith respect to MoꢀP_transobserved for [MoX(CO)-

(dppe)Cp] (X = Br,³Cl²¹) is not seen in 5b, 6a, or 6b. The

MoꢀCO bond length is sensitive to the identity of the Cp ligand,

with shorter bond distances normally observed for the more

electron rich Cp* complexes.

A key structural feature of four-leg piano stool systems

[ML₄Cp⁰] is distortion of the positions of the tetrapodal L ligands

out of the pseudosquare plane. These distortions can be quantiﬁed

by consideration of (i) the angles between mutually trans ligands

and (ii) the parameter θ²²(also designated R²³), which deﬁnes the

Cp°ꢀMoꢀ(Ligand) angle (Cp° = centroid of the Cp⁰ring).

These data for the alkynyl complexes 5b, 6a/b, 8a/b, and 9b

Inspection of Table 4 reveals that there is a much greater

disparity in the magnitudes of the trans angles in the dppe

complexes 5b and 6a/b than for the PMe₃complexes 8a/b

and 9b. For example, in [Mo(CtCPh)(CO)(dppe)Cp*], 5b,

the trans angles diﬀer by more than 40° [140.9° vs 97.6°],

whereas in trans-[Mo(CtCPh)(CO)(PMe₃)₂Cp*], 8b, the dif-

ference is less than 1° [117.9° vs 117.0°]. A similar trend is

observed for the halide derivatives 1a and 4b⁰, although here the

diﬀerence in trans angles for 4b⁰is rather larger. The dppe alkynyl

complexes 5b and 6a/b therefore exhibit a much larger distortion

in molecular geometry away from the pseudo-C_4vsymmetry of a

four-legged piano stool toward C_2vthan the related trans-PMe₃

systems 8a/b and 9b. Considering now the Cp°ꢀMoꢀ(Ligand)

or θ parameters, a variation in the approximate range 104ꢀ141°

is observed. Speciﬁc ligands can adopt θ values over a signiﬁcant

3766

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Figure 5. Plot of the molecular structure of 7b showing the atom-

labeling scheme. Key bond lengths (Å) and angles (deg): Mo(1)ꢀC(1)

2.137(4); C(1)ꢀC(2) 1.198(6); Mo(1)ꢀC(19) 1.953(5); Mo(1)ꢀC-

(20) 1.969(5); Mo(1)ꢀP(1) 2.451(1); C(1)ꢀMo(1)ꢀP(1) 74.0(1);

C(1)ꢀMo(1)ꢀC(19) 74.7(2); C(1)ꢀMo(1)ꢀC(20) 126.1(2);

P(1)ꢀMoC(19) 113.0(2); P(1)ꢀMo(1)ꢀC(20) 76.8(2).

Figure 3. Plot of the molecular structure of 8a showing the atom-

labeling scheme.

Under the conditions given in Table 5, each of the complexes

undergoes a diﬀusion-controlled, chemically reversible, one-

electron oxidation with the separation between cathodic and

anodic peak potentials comparable to that determined for the

internal ferrocene standard. The electrochemistry of the majority

of the halide complexes 1 to 4 has been reported previously,^10,13,26

and the literature data are included in Table 5, but E_1/2values were

redetermined in the current work to provide a self-consistent set

of values for comparison with the alkynyl analogues. A second

irreversible oxidation was observed at higher potentials, as de-

scribed previously for trans-[MoCl(CO)(PMe₃)₂Cp*], 4b;¹³the

potential for this process is reported as E_p(A) in Table 5,

determined at a scan rate of 100 mV s^ꢀ1

.

Figure 4. Plot of the molecular structure of 8b showing the atom-

labeling scheme.

The E_1/2values for the ﬁrst oxidation of [MoX⁰(CO)(L₂)Cp⁰]

show a dependence upon X⁰, L₂, and Cp⁰. Consideration of

[MoCl(CO)(dppe)Cp], 1a, and trans-[MoCl(CO)(PPh₃)₂Cp],

3a, suggests that the trans-phosphine arrangement of 3a leads to a

reduction in E_1/2of approximately 40 mV. Similarly, the re-

placement of Cp by Cp* results in a shift of E_1/2to negative

potential by approximately 100 mV, although the magnitude of

the change is slightly larger for the dppe series of complexes.

Comparison of the halide/phenyl-alkynyl pairs [MoX⁰(CO)-

(dppe)Cp] (1a with 5a) and trans-[MoX⁰(CO)(PMe₃)₂Cp*]

(4b with 8b) demonstrates that E_1/2is shifted slightly negative by

the replacement of Cl by CtCPh; a similar trend is observed for

[MoX⁰(dppe)(η-C₇H₇)] (E_1/2(V) vs FeCp₂/[FeCp₂]⁺in

CH₂Cl₂; X⁰= Cl, ꢀ0.61 V; X⁰= CtCPh, ꢀ0.72 V). However,

this feature is not reproduced in the [MoX⁰(CO)(dppe)Cp*]

series, for which the alkynyl complexes 5b and 6b are slightly

harder to oxidize than the chloride analogue 1b; this result may

indicate an enhanced alkynyl contribution to the redox orbital in

these examples. The absolute magnitudes of the E_1/2values for

the bis-phosphine alkynyl complexes 5a/b, 6a/b, 8a/b, and 9b lie

intermediate between the potentials for [Ru(CtCPh)

(dppe)Cp*] (ꢀ0.16 V vs FeCp₂/[FeCp₂]⁺in CH₂Cl₂), in which

the redox process features a substantial contribution from the alkynyl

ligand,^5aand [Mo(CtCPh)(dppe)(η-C₇H₇)] and [Fe(CtCPh)

(dppe)Cp*] (ꢀ0.72, ꢀ0.61 V vs FeCp₂/[FeCp₂]⁺in CH₂Cl₂,

respectively), in which the redox process is strongly metal based.^3a,7a

Spectroelectrochemical Analysis. To probe further the

character of the redox orbital in the alkynyl complexes

range dependent on the trans ligand and electron conﬁguration,

but in general, large θ parameters (typically 120ꢀ130°) are

exhibited by good acceptor ligands such as CO or PR₃, whereas

σ- or σ-/π- donor ligands such as halide and CtCR normally have

rather smaller θ values (typically 105ꢀ120°).²²The rationalization

for these observations is intimately connected with electronic

structure,^22,23and this will be reviewed at a later point in the paper.

However, a feature of the alkynyl complexes 5b, 6a/b, 8a/b, and 9b

is the combination of a double-faced π-acceptor ligand (CO) with a

good σ/π-donor ligand (CtCR) in cis or trans arrangements,

respectively. The salient θ parameters presented in Table 4 concern

θ(X⁰) and θ(P_cis) (i.e., the phosphorus located trans to the CO

ligand) for the dppe alkynyl complexes 5b and 6a/b. In particular for

the Cp* derivatives 5b and 6b, the small θ(CtCR) and large

θ(P_cis) angles lie close to the outer limits of observed values for

[ML₄Cp⁰] and indicate a signiﬁcant distortion away from the parent

pseudo-C_4vmolecular symmetry.

Electrochemistry. To commence investigations on the redox

chemistry of [Mo(CtCR)(CO)(L₂)Cp⁰], the cyclic voltammetry

of complexes 5b, 6a/b, 8a/b, and 9b at a glassy carbon electrode in

CH₂Cl₂/0.2 M [BuⁿN] PF₆was examined; previous electroche-

4

mical studies on cyclopentadienyl molybdenum alkynyl complexes

are restricted to the tricarbonyl derivatives [Mo(CtCPh)(CO)₃-

Cp⁰].²⁵The results are presented in Table 5, alongside data for the

corresponding halide complexes [MoX(CO)(L₂)Cp⁰], which have

been included for comparison.

3767

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Table 4. Analysis of Angular Parameters in [MoX⁰(CO)(L₂)Cp⁰] (X⁰= Cl or CtCR)^a

geometric trans angles (deg)

Cp°ꢀMoꢀ(Ligand) (deg)

complex

X⁰ꢀMoꢀP_trans

P_cisꢀMoꢀCO

X⁰ꢀMoꢀCO

P_cisꢀMoꢀP_cis

θ(X⁰)

θ(CO)

θ(P_trans

)

θ(P_cis

141.3

)

5b

6a

6b

1a

8a

8b

9b

4b⁰

140.91(7)

136.0(2)

134.8(1)

142.4(2)

97.60(8)

108.0(3)

104.4(1)

113.7(5)

104.0

106.9

105.0

106.8

118.2

121.1

114.4

111.9

120.4

125.0

120.6

121.5

126.8

121.0

124.0

117.8

115.1

116.8

120.2

110.2

126.3

133.4

124.8

115.0(2)

117.9(1)

121.61(9)

130.4(2)

123.24(6)

116.97(3)

113.79(2)

116.6(1)

117.0, 119.3

121.0, 121.9

123.1, 122.6

121.2, 122.1

^aDeﬁnitions of P_trans, P_cisas in Table 3.

Table 5. Cyclic Voltammetric Data for [MoX(CO)(L₂)Cp⁰]

Table 6. Infrared Spectroscopic Data (cm^ꢀ1) for the Com-

plexes [MoX⁰(CO)(L₂)Cp⁰]ⁿ⁺(n = 0 or 1; X⁰= Cl or CtCR;

L₂= 2 PMe₃or dppe, Cp⁰= Cp or Cp*)

(X⁰= halide, CtCR; L₂= 2 PMe₃or dppe; Cp⁰= Cp, Cp*)^a

compound E_1/2(V) (this work) E_p(A) (V)

E_1/2(V) (literature)

n = 0

n = 1

1a

1b

2a

3a

4b

5a

5b

6a

6b

8a

8b

9b

ꢀ0.24

ꢀ0.46

ꢀ0.23

ꢀ0.28

ꢀ0.54

ꢀ0.29

ꢀ0.41

ꢀ0.31

ꢀ0.44

ꢀ0.48

ꢀ0.56

ꢀ0.57

0.69

0.48

0.72

0.83

0.75

0.53

0.45

0.42

0.48

0.45

0.61

0.55

ꢀ0.25^b(26)

ꢀ0.44^c(10)

ꢀ0.24^b(26)

ν(CO) ν(CtC) ν(CO)

ν(CtC) Δν(CO) Δν(CtC)

1a^a1847 (1853)

1b^a1822 (1835)

4b^a1776 (1782)

5b^b1828

2013 (2002)

1981 (1971)

1929 (1920)

166 (149)

159 (136)

153 (138)

ꢀ0.48^c(10)ꢀ0.54^b(13)

2065 1969

2021 141

2012 143

2045 156

2047 159

ꢀ44

ꢀ56

ꢀ11

ꢀ9

6b^b1828

8b^b1776

9b^b1772

2068 1971

2056 1931

^aData recorded in CH₂Cl₂by generation of radicals in situ with

[FeCp₂]PF₆or (shown in parentheses) on isolated samples in thf.¹⁰

^bSpectroelectrochemical measurement in 0.1 M [BuⁿN]PF₆/CH₂Cl₂.

4

^aAll potentials are reported with reference to the FeCp₂/[FeCp₂]⁺

couple (E_1/2= 0.00 V). Experimental conditions (this work): 0.2 M

[BuⁿN]PF₆/CH₂Cl₂solutions at a glassy carbon working electrode.

redox-related family of compounds.²⁷In the case of metal alkynyl

complexes, the characteristic, IR-active ν(CtC) band reﬂects a

convolution of σ/π-donation, π-back-bonding, and physical/

kinematic eﬀects. Nevertheless, the changes in ν(CtC) that

occur as a result of a redox change within a series of closely

related alkynyl complexes can be used to assess the degree of

involvement of the alkynyl ligand in the redox orbital,^4a,b,28

especially when coupled with observation of other IR-active

bands elsewhere in the molecule.^6c,29In the case of [Mo-

(CtCR)(CO)(L₂)Cp⁰]ⁿ⁺in addition to the ν(CtC) band,

the ν(CO) band oﬀers a spectroscopic handle not available to

analogous studies on the d⁶systems [Mo(CtCR)(dppe)-

(η-C₇H₇)]ⁿ⁺and [M(CtCR)(dppe)Cp*]ⁿ⁺(M = Fe or Ru).

Guided by the results of the cyclic voltammetry, an IR

spectroelectrochemical investigation was carried out on the bis-

phosphine alkynyl complexes 5a/b, 6a/b, 8a/b, and 9b. The 17-

electron radicals formed from the Cp complexes 5a, 6a, and 8a

proved to be too reactive to be accessible to room-temperature,

spectroelectrochemical investigations. However the radicals de-

rived from the Cp* analogues 5b, 6b, 8b, and 9b exhibited

enhanced stability, suﬃcient for study in the spectroelectrochem-

ical cell. In each case the stability of the radical cation (and hence

the validity of ν(CO) and ν(CtC) data) was established by

back-reduction, which resulted predominantly in recovery of the

IR spectrum assigned to the 18-electron precursor, although

small quantities of secondary products were also observed. The

IR data obtained and the shifts in carbonyl and alkynyl stretching

4

E_p(A) = irreversible oxidation, at 100 mV s^ꢀ1. ^bIn CH₂Cl₂. ^cIn thf.

[Mo(CtCR)(CO)(L₂)Cp⁰], the spectroscopic properties of

the 17-electron Mo(III) radical cations [Mo(CtCR)(CO)

(L₂)Cp⁰]⁺invite examination. One approach to this objective

is the direct chemical synthesis and isolation of the required

radicals as achieved for [Mo(CtCR)(dppe)(η-C₇H₇)]⁺,

[Fe(CtCR)(dppe)Cp*]⁺, and [MoCl(CO)(L₂)Cp*]⁺(L₂=

dppe, 2PMe₃). Reaction of representative examples of [Mo-

(CtCR)(CO)(L₂)Cp⁰] with one equivalent of [FeCp₂]PF₆in

solution in cold (ꢀ40 °C) CH₂Cl₂resulted in an immediate

color change to deep turquoise-blue. However on slow warming

to ambient temperature, the blue coloration faded to brown, and

monitoring by solution IR spectroscopy revealed only decom-

position products. The exception to these observations was 17-

electron

trans-[Mo(CtCC₆H₄-4-Me)(CO)(PMe₃)₂Cp*]⁺,

[9b]⁺, which persisted in solution for several minutes at room

temperature; this derivative therefore defines the variables (R =

C₆H₄-4-Me; L₂= trans-(PMe₃)₂; Cp⁰= Cp*) conferring opti-

mum stability to the radical cations [Mo(CtCR)(CO)(L₂)-

Cp⁰]⁺. In view of the relatively poor thermal stability of the 17-

electron complexes [Mo(CtCR)(CO)(L₂)Cp⁰]⁺, the synthetic

studies were discontinued and the generation and observation of

the radicals by spectroelectrochemical methods pursued.

Spectroelectrochemical investigations permit the convenient

and rapid collection of spectroscopic data from each member of a

3768

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Figure 6. IR spectra of 8b/[8b]⁺generated in situ using spectroelectrochemical methods (CH₂Cl₂/0.1 M [BuⁿN]PF₆); — = 8b (with trace of [8b]⁺

4

also present); ---- = [8b]⁺.

frequencies resulting from one-electron oxidation [Δν(CO) and

Δν(CtC), respectively] are summarized in Table 6, and the

experimental spectra obtained for the redox pair trans-[Mo-

(CtCPh)(CO)(PMe₃)₂Cp*]ⁿ⁺, 8b/[8b]⁺, are presented in

Figure 6. Data for the related chloride complexes 1a/[1a]⁺,

1b/[1b]⁺, and 4b/[4b]⁺are also included to provide a direct

comparison of the Δν(CO) parameter. These latter data are either

literature values, recorded on isolated samples of the radicals in thf,¹⁰

or values obtained in the current work in CH₂Cl₂(to allow direct

comparison with alkynyl analogues) in which green-brown solutions

of the radicals [1a]⁺, [1b]⁺, and [4b]⁺were generated in situ by

addition of [FeCp₂]PF₆to solutions of the 18-electron precursors. It

became clear from these investigations that the halide radicals

[MoCl(CO)(L₂)Cp⁰]⁺are signiﬁcantly more stable than their alky-

nyl counterparts.

lower wavenumber for ν(CO) intrinsic to the Cp* derivatives. In all

cases considered, the magnitude of Δν(CtC) is relatively small, with

a maximum value of ꢀ56 cm^ꢀ1observed for [Mo(CtCC₆H₄-4-

Me)(CO)(dppe)Cp*], 6b. However, the results in Table 6 show that

the size of the negative shift in ν(CtC) resulting from one-electron

oxidation is molecular geometry dependent. Thus in the dppe

complexes 5b and 6b, the shift in ν(CtC) (in the range ꢀ44 to

ꢀ56 cm^ꢀ1for the alkynyl R substituents selected) is similar to that

found for [Fe(CtCR)(dppe)Cp*]ⁿ⁺for equivalent R substituents.^3a

By comparison a much smaller change in ν(CtC) is observed for the

trans-PMe₃derivatives 8b and 9b (ca.ꢀ10 cm^ꢀ1), more comparable⁷

to the behavior of [Mo(CtCR)(dppe)(η-C₇H₇)]ⁿ⁺. Taken to-

gether the Δν(CO) and Δν(CtC) data suggest that the redox

orbital in the complexes [Mo(CtCR)(CO)(L₂)Cp⁰] is strongly

metal based but with some alkynyl character, particularly in the dppe

complexes 5b and 6b.

Previous investigations on the UVꢀvisible spectra of metal alkynyl

complexes [Fe(CtCR)(dppe)Cp*]ⁿ⁺and [Mo(CtCR)(dppe)(η-

C₇H₇)]ⁿ⁺(n = 0 or 1) have demonstrated^3b,7athe operation of charge

transfer bands involving the alkynyl ligand with excitation energies in

the visible region. In the neutral 18-electron complexes these are

MLCT bands with energies at the blue end of the visible region,

whereas in the 17-electron radicals, strong LMCT bands are observed

with energies around 18 000 cm^ꢀ1(550 nm) giving rise to a deep

green or blue coloration. The intense turquoise-blue color of solutions

of the 17-electron radicals formed at low temperature in the pre-

liminary synthetic investigations on [Mo(CtCR)(CO)(L₂)Cp⁰]⁺

suggested that analogous charge transfer processes may occur in these

complexes. To investigate further, the UVꢀvisible spectra of the Cp*

alkynyl complexes 5b, 6b, 8b, and 9b and the corresponding radicals

were recorded using spectroelectrochemical methods; the experimen-

tal spectra for trans-[Mo(CtCC₆H₄-4-Me)(CO)(PMe₃)₂Cp*]ⁿ⁺,

9b/ [9b]⁺, are illustrated in Figure 7, with all data summarized

in Table 7.

One-electron oxidation of all complexes of the type [MoX⁰-

(CO)(L₂)Cp⁰] (X⁰= Cl or CtCR) results in a shift in ν(CO) to

higher wavenumber by 140ꢀ160 cm^ꢀ1, indicative of signiﬁcant

metal character in the redox orbital in all cases.³⁰However, a

slightly smaller shift in ν(CO) is observed for the alkynyl

complexes [Mo(CtCR)(CO)(dppe)Cp*], 5b and 6b, a feature

of signiﬁcance when considered together with shifts in ν(CtC);

see below. A more direct measure of the extent of the alkynyl

contribution to the redox orbital is provided by the shift in

ν(CtC) following one-electron oxidation. For example the

magnitude of Δν(CtC) resulting from the metal centered, one-

electron oxidation of [Mo(CtCPh)(dppe)(η-C₇H₇)] (ꢀ13 cm^ꢀ1

in CH₂Cl₂)^7acontrasts with the corresponding parameter of

ꢀ143 cm^ꢀ1(CH₂Cl₂) observed for oxidation of [Ru(CtCPh)

(dppe)Cp*], where the redox process results in signiﬁcant depopula-

tion of the alkynyl π-bonding orbitals.^4aThe key Δν(CtC) para-

meter was not readily determined for all complexes of formulation

[Mo(CtCR)(CO)(L₂)Cp⁰]ⁿ⁺because of overlap of ν(CtC) and

ν(CO) stretches in the 17-electron radicals, a problem compounded

by reduction in the intensity of the ν(CtC) band in the oxidized

products. However, in the case of the Cp* complexes selected for

investigation, determination of Δν(CtC) was facilitated by the

The key feature in the spectroelectrochemically generated

UVꢀvisible spectra of 5b/[5b]⁺, 6b/[6b]⁺, 8b/[8b]⁺, and

9b/[9b]⁺is the appearance of a new band in the visible region

3769

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

in the spectra of the 17-electron radicals ([5b]⁺, 15 800 cm^ꢀ1

633 nm; [6b]⁺, 15 770 cm^ꢀ1, 634 nm; [8b]⁺, 16 700 cm^ꢀ1

,

dppe ligand and a series of satellites from the spin-active

molybdenum isotopes ⁹⁵Mo and ⁹⁷Mo. The hyperﬁne couplings

to ^95/97Mo and ³¹P are in close agreement with those previously

reported and similar to those determined for the related complex

[MoCl(dppe)(η-C₇H₇)]⁺(a_iso, G, CH₂Cl₂solution, 243 K: Mo,

40.0; ³¹P, 23.2) in which the unpaired electron is strongly metal

centered.³¹Additional hyperﬁne interactions, superimposed

upon the basic pattern, are clearly evident in Figure 8a,b. For

the Cp* complex [1b]⁺, the spectrum can be simulated by

inclusion of additional hyperﬁne coupling to ³⁵Cl/³⁷Cl, but for

[1a]⁺, the spectrum exhibits further complexity arising from

hyperﬁne coupling to the hydrogens of the Cp ring, a feature also

observed in the EPR spectrum of the 17-electron radical

[Mo(dppe)₂Cp]²⁺.³²The EPR spectrum of the bromide deriva-

tive [2a]⁺(Figure 8c) conﬁrms the contribution of the halide

ligand, but in this case, the much larger hyperﬁne coupling to Br

(12.5 G) leads to signiﬁcant perturbation of the spectral pattern.

The key spectral feature of the trans-phosphine chloride

complexes [MoCl(CO)(PPh₃)₂Cp]⁺, [3a]⁺, and [MoCl(CO)-

(PMe₃)₂Cp*]⁺, [4b]⁺, is a 1:2:1 triplet conﬁrming that the trans-

phosphine geometry is retained in the 17-electron radicals. In

addition to hyperﬁne coupling to ^95/97Mo and ³¹P, superimposed

coupling to Cl (and in [3a]⁺, H of the Cp ring) was also observed

albeit with poorer resolution than for the dppe complexes. The

hyperﬁne values computed for trans-[MoCl(CO)(PR₃)₂Cp⁰]⁺

appear almost invariant with the identity of PR₃and Cp⁰,

although a_iso(Mo) values are approximately 3 G smaller than

for the corresponding dppe complexes.

599 nm; and [9b]⁺, 16 000 cm^ꢀ1, 625 nm). Similar absorptions

in the visible region of 17-electron alkynyl complexes have been

reported previously (for example [Mo(CtCPh)(dppe)(η-

C₇H₇)]⁺, 16 900 cm^ꢀ1, 592 nm)^7aand assigned with the aid of

a TD-DFT treatment to an alkynyl-to-metal LMCT process.

EPR Investigations. The 17-electron radicals [MoX⁰(CO)(L₂)-

Cp⁰]⁺(X⁰= halide or CtCR) were further investigated by X-band

solution EPR spectroscopy in CH₂Cl₂. Previous work on the EPR

spectra of isolated samples of the chloride derivatives [MoCl-

(CO)(dppe)Cp]⁺, [1a]⁺, [MoCl(CO)(dppe)Cp*]⁺, [1b]⁺, and

trans-[MoCl(CO)(PMe₃)₂Cp*]⁺, [4b]⁺, recorded in solution in thf

reports isotropic spectra with resolved hyperfine coupling to

^95/97Mo and ³¹P.¹⁰In the current investigation, samples of the 17-

electron radicals were generated by in situ oxidation with [FeCp₂]-

PF₆in CH₂Cl₂followed by immediate cooling to 243 K. These

modified conditions allowed observation of the full range of radical

cations, including the unstable alkynyl Cp complexes. Additionally,

enhanced spectral resolution was obtained leading in the case of

[MoCl(CO)(dppe)Cp]⁺, [1a]⁺, to the observation of hyperfine

coupling both to the Cl ligand and to H of the Cp ring. A sample of

[1a]⁺was also generated from 1a and [FeCp₂]PF₆in thf. The

resulting EPR spectrum was almost identical to that reported for an

isolated sample of [1a]⁺and to the spectrum obtained in CH₂Cl₂

except that the hyperfine couplings to Cl and H of the Cp ring were

now unresolved. A full analysis of the EPR spectral parameters,

confirmed by spectral simulation, is presented in Table 8.

The solution EPR spectra of the dppe halide derivatives [1a]⁺,

[1b]⁺, and [2a]⁺exhibit excellent resolution of hyperﬁne cou-

plings, as shown in Figure 8aꢀc, respectively. For [1a]⁺and

[1b]⁺, the underlying spectral pattern is a doublet of doublets

due to coupling to the inequivalent phosphorus atoms of the

The EPR spectra of the alkynyl cyclopentadienyl complexes

[Mo(CtCR)(CO)(dppe)Cp]⁺(R = Ph, [5a]⁺, R = C₆H₄-4-Me,

[6a]⁺) are similar to the spectrum of the chloride analogue [1a]⁺,

Table 8. EPR Data for the 17-Electron Radicals

[MoX⁰(CO)(L₂)Cp⁰]⁺.^a

g_iso

/

a_iso(Mo)/ a_iso

(

³¹P₁)/ a_iso

(

³¹P₂)/

G

a_iso(other)/

G

[1a]⁺1.996

[1b]⁺1.999

[2a]⁺2.019

[3a]⁺1.998

[4b]⁺1.998

[5a]⁺1.999

[5b]⁺1.997

[6a]⁺1.999

[6b]⁺1.998

[8a]⁺2.005

[8b]⁺2.001

[9b]⁺2.001

31.0

25.5

28.5

27.5

26.4

15.5

26.0

15.8

25.0

26.0

27.9

27.0

18.0

24.0

23.8

20.5

23.6

20.2

20.0

25.2

14.3

18.3

15.0

18.0

24.0

14.4

6.0

1.9, 1.6 (Cl), 2.2 (H, Cp)

1.9, 1.6 (Cl)

12.5 (Br)

1.1, 1.4 (Cl), 2.6 (H, Cp)

14.0

5.8

20.0

25.2

Figure 7. UVꢀvisible spectra of 9b/ [9b]⁺generated in situ by spectro-

^aX-band solution spectra in CH₂Cl₂at 243 K; hyperﬁne couplings

electrochemical methods (CH₂Cl₂/0.1 M [BuⁿN]PF₆).

in Gauss.

4

Table 7. UVꢀVisible Data for the Complexes [Mo(CtCR)(CO)(L₂)Cp*]ⁿ⁺(n = 0 or 1)^a

complex

n = 0

n = +1

5b

6b

8b

9b

42 500 (29 000), 29 200 (11 200), 22 400, sh, (1300)

30 500 (12 160)

42 500 (29 000), 33 100, sh, (10 700), 25 000 (2500), 15 800 (1800)

15 770 (1370)

40 300, br, (13 960), 29 400 (10 540), 26 320, sh, (5460)

40 500 (14 500), 29 100 (9200), 24 800, sh, (3100)

^aν_max/cm^ꢀ1(ε/M^ꢀ1cm^ꢀ1) determined by spectroelectrochemical methods in 0.1 M [BuⁿN]PF₆/CH₂Cl₂.

35 700 (11 500), 23 400 (2430), 16 700 (1700)

42 200 (14 700), 35 500 (11 100), 25 900 (1700), 23 400 (1800), 16 000 (1500)

4

3770

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

were almost identical to the chloride derivatives [3a]⁺and [4b]⁺.

The principal 1:2:1 triplet pattern arising from hyperﬁne cou-

pling to two equivalent PMe₃ligands was observed, conﬁrming

retention of the trans-PMe₃geometry in the alkynyl radicals.

However, unlike the dppe complexes, the changes in a_iso(Mo)

and a_iso(P) resulting from exchange of Cl for CtCPh or Cp* in

place of Cp are very small.

Electronic Structure Calculations. The experimental inves-

tigations outlined above suggest that the redox orbital in

[Mo(CtCR)(CO)(L₂)Cp⁰] has substantial metal-centered

character, evident from the large increase in ν(CO) following

one-electron oxidation to the 17-electron radicals and the

correspondingly rather small negative shift in ν(CtC). How-

ever, EPR investigations on [MoX⁰(CO)(L₂)Cp⁰]⁺(X⁰= halide

or CtCR) indicate some spin delocalization onto the X⁰ligand,

either from the direct observation of a_iso(Cl/Br) in the halide

radicals [MoX⁰(CO)(L₂)Cp⁰]⁺or indirectly via the reduced

magnitude of the hyperfine couplings, a_iso(^95/97Mo) and a_iso-

(³¹P) in the Cp* alkynyl complexes [5b]⁺and [6b]⁺. Moreover

the two series of complexes [Mo(CtCR)(CO)(dppe)Cp⁰]ⁿ⁺

and trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰]ⁿ⁺exhibit distinctive

structural and spectroscopic characteristics with evidence for

enhanced participation of the alkynyl ligand in the redox orbital

of the dppe systems.

To rationalize these observations in terms of the electronic

structure of [Mo(CtCR)(CO)(L₂)Cp⁰], a computational study

was conducted at the DFT level using the B3LYP functional and

the def-SVP basis set; this level of theory was used to provide

consistency with previous investigations on [M(CtCPh)

(dppe)(η-C₇H₇)]ⁿ⁺(M = Mo^7aor W⁸). For purposes of compu-

tational eﬃciency, the model systems [Mo(CtCPh)(CO)

(dHpe)Cp], 5-H (dHpe = H₂PCH₂CH₂PH₂), and trans-[Mo-

(CtCPh)(CO)(PH₃)₂Cp], 8-H, were investigated as the

closed-shell, 18-electron complexes. The calculated complexes

are denoted -H to distinguish computational and experimental

systems.

Key bond length and angle parameters from the DFT-opti-

mized geometries of complexes 5-H and 8-H are summarized in

Table 9. The calculated structural data, including trans angles

across the tetrapodal ligand set, are in good agreement with the

crystallographically determined structures of the related experimen-

tal systems [Mo(CtCC₆H₄-4-Me)(CO)(dppe)Cp], 6a (given in

place of the phenyl-alkynyl derivative 5a, for which X-ray data are

not available), and trans-[Mo(CtCPh)(CO)(PMe₃)₂Cp], 8a,

respectively. The energies and composition of the principal frontier

orbitals (LUMO, HOMO, HOMOꢀ1, and HOMOꢀ2) are shown

in Table 10, and plots of these orbitals for 5-H and 8-H are presented

in Figures 10 and 11, respectively.

The electronic structures of the two model systems [Mo(Ct

CPh)(CO)(dHpe)Cp], 5-H, and trans-[Mo(CtCPh)(CO)-

(PH₃)₂Cp], 8-H, appear strikingly diﬀerent. This is a direct

consequence of the cis versus trans molecular geometry of the

two systems and not a result of the identity of the P-donor ligands

since calculations on the computational model species cis-[Mo-

(CtCPh)(CO)(PH₃)₂Cp] reveal an electronic structure analo-

gous to that of the dHpe complex 5-H. In both 5-H and 8-H, a

key aspect of electronic structure [not encountered for the widely

reported tripodal alkynyl complexes [M(CtCPh)(dppe)(η-L)]

(M = Fe, Ru, L = Cp; M = Mo, L = C₇H₇)] involves the bonding

interactions between ﬁlled metal d-orbitals and the empty CO

π*-level. The diﬀerent molecular geometries of 5-H and 8-H

require diﬀerent orbital interactions to optimize back-bonding

Figure 8. Fluid solution (CH₂Cl₂, 243 K), second derivative X-band

EPR spectra of (a) [MoCl(CO)(dppe)Cp]PF₆, [1a]PF₆;(b) [MoCl(CO)-

(dppe)Cp*]PF₆, [1b]PF₆; and (c) [MoBr(CO)(dppe)Cp]PF₆, [2a]PF₆.

although no hyperﬁne coupling to H of the Cp ring was observed

and hyperﬁne couplings to ^95/97Mo and ³¹P are slightly smaller.

However, substitution of Cp by Cp* produces a dramatic eﬀect

with very signiﬁcant reduction in a_iso(Mo) and a_iso(P), as evident

from a comparison of Figure 9a and b. Thus, in the Cp* complexes

[Mo(CtCR)(CO)(dppe)Cp*]⁺, [5b]⁺and [6b]⁺, a_iso(Mo) and

the averaged value of a_iso(P) are approximately one-half of the

corresponding parameters both for the Cp* chloride derivative [1b]⁺

and in the Cp alkynyl analogues [5a]⁺and [6a]⁺. Of particular note is

the very small hyperﬁne (ca. 6 G) to one of the phosphorus nuclei

in the Cp* alkynyl systems [5b]⁺and [6b]⁺; this eﬀect is observed

only for the combination of variables Cp⁰= Cp*, X⁰= CtCR in

[MoX⁰(CO)(dppe)Cp⁰]⁺. The reduced hyperﬁne couplings to Mo

and phosphorus in the pentamethylcyclopentadienyl alkynyl com-

plexes [5b]⁺and [6b]⁺may be indicative of enhanced delocalization

of spin density onto the alkynyl ligand.

In contrast with the dppe alkynyl complexes, the EPR spectra

of the PMe₃alkynyl complexes trans-[Mo(CtCR)(CO)-

(PMe₃)₂Cp⁰]⁺([8a]⁺and its Cp* analogues [8b]⁺and [9b]⁺)

3771

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Table 9. Selected Bond Lengths (Å) and Angles (deg) for the

Calculated Systems [Mo(CtCPh)(CO)(L₂)Cp], 5-H and

8-H, and Experimental Counterparts 6a and 8a^a

5-H

6a

8-H

8a

MoꢀC_R

C_RꢀC_β

MoꢀP

2.141

1.232

2.460,

2.456

1.970

2.134(9)

1.21(1)

2.148

1.235

2.447,

2.447

1.955

120.3

117.7

2.129(6)

1.221(9)

2.423(2),

2.426(2)

1.923(6)

123.23(6)

115.0(2)

2.428(2),

2.467(2)

1.97(1)

MoꢀCO

P_cisꢀMoꢀP_cis

C_RꢀMoꢀCO

P_cisꢀMo--CO

C_RꢀMoꢀP_trans

105.8

136.9

108.0(3)

136.0(2)

^aSee Table 3 for key to atom-labeling scheme.

Table 10. Energy and Composition of Frontier Orbitals in

the Calculated Systems [Mo(CtCPh)(CO)(L₂)Cp], 5-H

and 8-H

energy

%

complex

orbital

(eV) Mo Cp L₂CO C_RC_βPh

5-H LUMO

ꢀ0.81 35

ꢀ4.76 34

15 30

7

4

5

HOMO

5

4

8

3

5

2

6

9

12 20 19

HOMOꢀ1 ꢀ5.01 52

HOMOꢀ2 ꢀ5.88 31

8-H LUMO

HOMO

13

5

19

7

12

8

4

25

33

1

8

ꢀ0.78 17

ꢀ4.91 59

26

6

5

4

16

10

7

2

12

HOMOꢀ1 ꢀ5.08 41

HOMOꢀ2 ꢀ6.15 25

4

8

15 17

32

10

19

5

Figure 9. Fluid solution (CH₂Cl₂, 243 K), second derivative X-band EPR

spectra of (a) [Mo(CtCC₆H₄-4-Me)(CO)(dppe)Cp]PF₆, [6a]PF₆, and

(b) [Mo(CtCC₆H₄-4-Me)(CO)(dppe)Cp*]PF₆, [6b]PF₆.

antibonding interaction with the remaining alkynyl π-level; this

latter interaction is more eﬃcient in the xy plane, evident from

much greater alkynyl contribution (40%) to the orbital composi-

tion. HOMOꢀ2 (which is signiﬁcantly lowered in energy with

respect to HOMOꢀ1 and almost 60% localized on the alkynyl

ligand) involves metalꢀligand bonding interactions with both

the ﬁlled alkynyl π- and empty CO π*-levels. The transfer of

electron density from a ﬁlled alkynyl π-orbital to the empty π*-

level of the trans-CO ligand may be facilitated by the conﬁgura-

tion of HOMOꢀ2.

with the CO π*-orbitals, and this is reﬂected in the resulting

electronic structures.

The electronic structure of the more straightforward case, the

trans-PH₃complex 8-H, is considered ﬁrst; the principal com-

ponents of the frontier orbitals are illustrated in Figure 11. The

HOMO of 8-H features the metal d_z₂-orbital, and therefore the

local symmetry is deﬁned with the z axis coincident with a line

between the metal and the centroid of the cyclopentadienyl ring.

This arrangement of the d-orbital manifold, in which d_xy

contributes to the HOMOꢀ1 (just slightly lower in energy than

the d_z₂-based HOMO) and d_yz- and d_xz-orbitals are involved in

π-bonding interactions with the e₁-level of the Cp ligand

(identiﬁed as HOMOꢀ6 and HOMOꢀ14, respectively, in

Figure 11), is consistent with previous theoretical treatments

for four-leg piano stool systems.^23,33The HOMO of 8-H is

strongly metal centered (59%) with signiﬁcant components on

CO (16%) and C_βof the alkynyl ligand (12%). The principal

metalꢀligand interactions are bonding to the CO ligand and a

ﬁlledꢀﬁlled, antibonding interaction with the alkynyl π-orbital;

these ﬁlledꢀﬁlled overlaps are a recurrent feature of the HOMOs

of electron-rich metal alkynyl systems.^3b,4a,7aHowever in 8-H the

The frontier molecular orbitals of the cis-phosphine, dHpe

complex 5-H are shown in Figure 10. As for 8-H, interactions

with the ﬁlled alkynyl π- and empty CO π*-orbitals dominate the

composition of HOMO, HOMOꢀ1, and HOMOꢀ2, but the

energy ordering of the d-orbital manifold appears to be very

diﬀerent, with d_xyreplacing d_z₂as the frontier metal orbital

contributing to the HOMO (assuming a common coordinate

system in which the z direction is located along the metalꢀring

axis). However, further consideration shows that the electronic

structure of 5-H can be interpreted as a perturbation of the

structure of 8-H.

The HOMO of 5-H comprises a ﬁlledꢀﬁlled, antibonding

overlap between the alkynyl π-level and the metal d_xy-orbital,

equivalent to that observed in the HOMOꢀ1 of 8-H. This is a

strong interaction, similar to that found in the HOMO of

[M(CtCPh)(dppe)Cp] (M = Fe, Ru)^3b,4aand unconstrained

by symmetry or competition with a trans-carbonyl ligand.

Accordingly the HOMO of 5-H has increased alkynyl character

poor symmetry match of the alkynyl π-orbital with the metal d_z₂

-

orbital, combined with a competing bonding overlap with the

CO π*-level, prescribes only a weak metal alkynyl interaction. In

HOMOꢀ1, the d_xy-orbital similarly serves a dual function of

a bonding overlap with the CO π*-orbital and a ﬁlledꢀﬁlled

3772

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Figure 10. LUMO, HOMO, HOMOꢀ1, HOMOꢀ2, HOMOꢀ5, and HOMOꢀ6 of 5-H at B3LYP/SVP plotted as isosurfaces of 0.04 au.

(51%) and reduced metal (34%) and CO (4%) composition by

comparison with the HOMO of 8-H. The composition of

HOMOꢀ1 and HOMOꢀ2 of 5-H is not readily deﬁned in

terms of simple metal d-orbital components, although the “on

axis” z component of HOMOꢀ1 pointing directly toward the Cp

ring is easily recognized. As noted previously in the X-ray

structural studies, the complexes [Mo(CtCR)(CO)(dppe)

Cp⁰] (5b and 6a/b), in which the P-donor atoms are disposed

mutually cis, undergo a distortion of the molecular geometry

away from the idealized C_4vsymmetry of a square-based pyr-

amidal form toward C_2v, a feature reproduced in the calculated

structure of 5-H. This reduction in molecular symmetry from

pseudo-C_4vto C_2vpermits signiﬁcant mixing of the metal d_z₂- and

d_x₂_ꢀy₂-orbitals and, as previously proposed,²³leads to the forma-

tion of two new hybrid orbitals, directed along the yz and xz axes,

as manifest in HOMOꢀ1 and HOMOꢀ2 of Figure 10. En-

ergetically, the driving force for a rehybridization in the dHpe

system is the localization of metal orbitals in their interaction

with strong acceptor (CO) or strong donor (CtCR) ligands. In

HOMOꢀ1, the acceptor ligands (CO and the phosphine located

trans to CO), which are bent down away from the xy plane,

experience enhanced metal-to-ligand π-back-bonding in the yz

plane (evident from the 13% CO character of this orbital); this is

the origin of the large θ values [θ(CO), θ(P_cis)] for these ligands,

as shown in Table 4. By contrast in HOMOꢀ2, the donor ligands

(CtCR and the phosphine trans to the alkynyl ligand, P_transin

Table 4) are inclined upward toward the xy plane (small θ

values) to optimize the bonding interaction between the ﬁlled

alkynyl π-orbital and the metal hybrid acceptor orbital directed in

the xz plane. An important result of the rehybridization in 5-H is

that in HOMOꢀ1 the metalꢀalkynyl interaction is nonbonding,

thus avoiding the ﬁlledꢀﬁlled antibonding interaction in the

alternative electronic structure of 8-H. An analogous rehybridi-

zation of the trans-phosphine complex 8-H is not energetically

favorable because the trans-disposed CO acceptor and CtCR

donor ligands must share the same metal orbital.

The electronic structures outlined above provide the basis for

an understanding of the redox behavior of the experimental

systems with cis-phosphine (5a/b and 6a/b) and trans-phos-

phine (8a/b and 9b) molecular geometries. Although the

HOMOs of both 5-H and 8-H are quite strongly metal centered

(Table 10), the relative contribution of the alkynyl ligand in the

dHpe system 5-H is much greater than for the trans-PH₃

counterpart, 8-H (metal: alkynyl % compositions, 5-H: 34:51;

8-H: 59:15). The reduced metal character and increased alkynyl

composition of the HOMO of the dHpe complex 5-H is

consistent with the rather larger negative shift in ν(CtC)

resulting from one-electron oxidation of the experimental sys-

tems [Mo(CtCR)(CO)(dppe)Cp*] (5b, 6b) by comparison

with trans-[Mo(CtCR)(CO)(PMe₃)₂Cp*] (8b, 9b).

Finally the poor thermal stability of the 17-electron alkynyl

radicals [Mo(CtCR)(CO)(L₂)Cp⁰]⁺should be addressed.

Given the small shifts in ν(CtC) resulting from one-electron

oxidation, especially for the trans-phosphine complexes, the

diﬃculty in isolation of the 17-electron radical cations is surpris-

ing when compared with the cycloheptatrienyl complexes

3773

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Figure 11. LUMO, HOMO, HOMOꢀ1, HOMOꢀ2, HOMOꢀ6, and HOMOꢀ14 of 8-H at B3LYP/SVP plotted as isosurfaces of 0.04 au.

[Mo(CtCR)(dppe)(η-C₇H₇)]⁺, which are stable systems for a

wide range of alkynyl substituents R.⁷Two factors may con-

tribute to the limited stability of [Mo(CtCR)(CO)(L₂)

Cp⁰]⁺. First the cyclopentadienyl complexes incorporate a labile

carbonyl ligand, which is activated to elimination or substitution by

one-electron oxidation. However, this in itself cannot explain the rapid

decomposition of the alkynyl radicals since the chloride analogues

[MoCl(CO)(L₂)Cp*]⁺, although reactive, are isolable.¹⁰The addi-

tional function of the alkynyl ligand may be to facilitate a decom-

position pathway, promoted by the formally Mo(III), d³metal center,

involving conversion of the σ-bonded alkynyl to a π-bonded four-

electron alkyne ligand, thus driving elimination of the CO ligand.

a reversible one-electron oxidation on the electrochemical time

scale. Although the resulting 17-electron radicals were too

reactive for chemical isolation, further investigations by spectro-

electrochemical IR and UVꢀvisible techniques were accom-

plished for the more stable Cp* derivatives. Changes in ν(CO)

and ν(CtC) resulting from one-electron oxidation provide a

dual probe of the redox process, which is strongly metal based, as

evidenced by shifts in ν(CO) to higher wavenumber, by 140ꢀ

160 cm^ꢀ1. However the response of ν(CtC) to one-electron

oxidation diﬀers between the two groups of complexes [Mo-

(CtCR)(CO)(dppe)Cp*]ⁿ⁺and trans-[Mo(CtCR)(CO)-

(PMe₃)₂Cp*]ⁿ⁺(n = 0 or 1), with the rather larger negative shift

for [Mo(CtCR)(CO)(dppe)Cp*]ⁿ⁺indicative of greater alky-

nyl character in the redox orbital, a conclusion supported by the

large reductions in hyperﬁne coupling to Mo and P observed in

the solution EPR spectra of [Mo(CtCR)(CO)(dppe)Cp*]⁺.

DFT, electronic structure calculations on the model complexes

[Mo(CtCR)(CO)(dHpe)Cp] and trans-[Mo(CtCR)(CO)-

(PH₃)₂Cp] reveal a switch in electronic structure dependent on

the complex coordination geometry. In trans-[Mo(CtCR)-

(CO)(PH₃)₂Cp], the HOMO incorporates a symmetry-re-

stricted antibonding interaction between the metal d_z₂-orbital

and the ﬁlled alkynyl π-orbital. By contrast in [Mo(Ct-

CR)(CO)(dHpe)Cp], a structural distortion leads to a HOMO

with metal d_xycharacter and enhanced alkynyl contribution in

accord with the properties of the experimental systems. This

’ CONCLUSIONS

Synthetic routes to bis-phosphine-substituted cyclopentadie-

nyl molybdenum alkynyl complexes [Mo(CtCR)(CO)(dppe)

Cp⁰] and trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰] (R = Ph or

C₆H₄-4-Me, Cp⁰= Cp or Cp*) have been developed. The new

complexes have been characterized by a range of spectroscopic

methods and representative examples investigated by X-ray

structural studies, which reveal signiﬁcant structural distortions

away from pseudo-C_4vsymmetry in complexes of the type

[Mo(CtCR)(CO)(dppe)Cp*]. Cyclic voltammetric investiga-

tions show that each of the complexes [Mo(CtCR)(CO)

(dppe)Cp⁰] and trans-[Mo(CtCR)(CO)(PMe₃)₂Cp⁰] undergoes

3774

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

work indicates the potential for a switchable redox response, via a

perturbation in electronic structure controlled by changes in

molecular geometry.

Preparation of [MoBr(CO)(dppe)Cp] (2a). Complex 2a was prepared

by an identical procedure to that described for 1a from [MoBr-

(CO)₃Cp] (0.50 g, 1.54 mmol) and dppe (0.92 g, 2.31 mmol). The

1

product was obtained as an orange-red solid: yield 0.45 g (44%). H

NMR (CDCl₃): δ 1.55 (br, 1H, CH₂), 2.21 (br, 1H, CH₂), 2.56 (br, 2H,

CH₂), 4.37 (s, 5H, Cp), 7.22 ꢀ 7.74 (m, 20H, Ph). ³¹P{¹H} NMR

(CDCl₃): δ 92.4 (d, J_PP= 38.9 Hz, dppe), 64.5 (d, J_PP= 38.9 Hz, dppe).

IR (CH₂Cl₂): ν(CtO) 1849 cm^ꢀ1. MALDI-MS (m/z): 639 [(M ꢀ

CO)]⁺. Anal. Calcd (%) for C₃₂H₂₉OMoBrP₂: C, 57.6; H, 4.4. Found:

C, 57.3; H, 3.8.

Preparation of [MoCl(CO)(PPh₃)₂Cp] (3a). A mixture of [MoCl(CO)₃-

Cp] (0.50 g, 1.79 mmol) and PPh₃(2.34 g, 8.91 mmol) was dissolved in

toluene (60 cm³), and the solution was refluxed for 18 h then evaporated to

dryness. The residue, dissolved in CH₂Cl₂, was transferred to an n-hexane-

alumina chromatography column, and the product eluted as an orange-red

band with hexane/CH₂Cl₂(9:1 v:v) as eluant. Reduction of solvent volume

in vacuo and addition of further hexane resulted in precipitation of the product

as an orange-red solid: yield 0.801 g (60%). ¹H NMR (CDCl₃): δ 4.73 (t,

5H, J_HP=1.0Hz, Cp), 7.12ꢀ7.63 (m, 36H, Ph). ³¹P{¹H} NMR (CDCl₃):δ

57.5 (s, PPh₃). IR (CH₂Cl₂): ν(CtO) 1792 cm^ꢀ1. MALDI-MS (m/z):

750, [M]⁺; 722[(M ꢀ CO)]⁺;715[(M ꢀ Cl)]⁺; 488[(Mꢀ PPh₃)]⁺; 460

[(M ꢀ CO ꢀ PPh₃)]⁺. Anal. Calcd (%) for C₄₂H₃₅OMoClP₂: C, 67.4; H,

4.7. Found: C, 67.2; H, 4.5.

’ EXPERIMENTAL SECTION

General Procedures. The preparation, purification, and reactions

of the complexes described were carried out under dry nitrogen using

standard Schlenk techniques. The complexes [MoCl(CO)₃Cp⁰] (Cp⁰=

Cp, Cp*)³⁴and [Mo(CtCPh)(CO)₃Cp⁰] (Cp⁰= Cp, Cp*)³⁵were

prepared by published procedures, and the alkynes HCtCPh and

HCtCC₆H₄-4-Me were purchased from commercial sources. NMR

spectra were recorded from CDCl₃solutions, unless otherwise stated, on

Varian Inova 300 or 400 spectrometers at room temperature and

referenced against solvent resonances (¹H, ¹³C) or external H₃PO₄

(³¹P). Infrared spectra were obtained on Perkin-Elmer FT RX1 or

Nicolet Avatar spectrometers. Mass spectra were recorded using Ther-

mo Quest Finnigan Trace GC/MS or Thermo Electron Finnigan LTQ

FT mass spectrometers. MALDI mass spectra were recorded using a

Micromass/Waters TOF Spec 2E instrument. Microanalyses were

conducted by the staff of the Microanalytical Services of the School of

Chemistry, University of Manchester. Cyclic voltammograms were

recorded (ν = 100 mV s^ꢀ1) from 0.2 M [BuⁿN]PF₆, CH₂Cl₂solutions

4

ca. 1 ꢁ 10^ꢀ4M in analyte using a three-electrode cell equipped with a

glassy carbon disk working electrode, Pt wire counter electrode, and

Ag/AgCl reference electrode. All redox potentials are reported with

reference to an internal standard of the ferrocene/ferrocenium couple

(FeCp₂/[FeCp₂]⁺= 0.00 V). UVꢀvisible and IR spectroelectrochem-

ical experiments were performed at room temperature with an airtight

OTTLE cell of Hartl design^27aequipped with Pt minigrid working and

counter electrodes, a Ag wire reference electrode, and CaF₂windows

using either a Nicolet Avatar spectrometer or a Perkin-Elmer Lambda

900 spectrophotometer. EPR experiments were conducted on a Bruker

BioSPin EMX microspectrometer at X-band (9 GHz); spectra were

recorded at 243 K and are the average of 16 scans. Spectral analysis and

simulation was carried out using Bruker WinEPR software (Bruker

Biospin Ltd.).

Preparation of [MoCl(CO)(PMe₃)₂Cp*] (4b). A mixture of [MoCl-

(CO)₃Cp*] (0.50 g, 1.49 mmol) and PMe₃(3.4 cm³of a 1.0 M solution

in toluene, 3.4 mmol) was dissolved in toluene (60 cm³), and the

solution was refluxed for 18 h then evaporated to dryness. The residue,

dissolved in CH₂Cl₂, was transferred to an n-hexane-alumina chroma-

tography column, and the product eluted as an orange-red band with

hexane/CH₂Cl₂(9:1 v:v) as eluant. Recrystallization from pentane at

ꢀ20 °C gave the product as an orange-red solid: yield 0.20 g (30%). ¹H

NMR (CDCl₃): δ 1.32 (m, 18H, PMe₃), 1.72 (s, 15H, Cp*). ³¹P{¹H}

NMR (CDCl₃): δ 18.1 (s, PMe₃). ES-MS (m/z): 448, [M]⁺. IR

(CH₂Cl₂): ν(CtO) 1776 cm^ꢀ1. Anal. Calcd (%) for C₁₇H₃₃OMoClP₂:

C, 45.7; H, 7.4. Found: C, 45.9; H, 7.9.

Preparation of [Mo(CtCPh)(CO)(dppe)Cp] (5a). A mixture of

[MoCl(CO)(dppe)Cp] (0.50 g, 0.80 mmol) and HCtCPh (0.50 g,

4.90 mmol) in methanol (100 cm³) was refluxed for 1.5 h to give a green

solution of [Mo(HCtCPh)(dppe)Cp]Cl. Carbon monoxide gas was

bubbled through the solution for 10 min to give an orange solution of the

vinylidene [Mo(CdCHPh)(CO)(dppe)Cp]Cl [ν(CO) (CH₂Cl₂)

1902 cm^ꢀ1], which was treated with NaOMe (0.50 g, 9.3 mmol) to

give a yellow solution, which was evaporated to dryness. The residue,

dissolved in CH₂Cl₂, was transferred to a hexane-alumina column, and

the product eluted as a yellow band with hexane/CH₂Cl₂/acetone

(2:2:1 v:v:v) as eluant. Reduction in solvent volume in vacuo and

addition of further hexane resulted in precipitation of the product as a

Preparations. Preparation of [MoCl(CO)(dppe)Cp] (1a). A solu-

tion of [MoCl(CO)₃Cp] (2.40 g, 8.60 mmol), dissolved in hot toluene

(100 cm³) was added dropwise over a period of 90 min to a solution of

dppe (3.70 g, 9.3 mmol) in refluxing toluene (50 cm³). After completion

of the addition, reflux was continued for a further 3 h. Then the reaction

mixture was evaporated to dryness. The residue, dissolved in CH₂Cl₂,

was transferred to an n-hexane-alumina chromatography column, and

the product eluted as an orange-red band with hexane/CH₂Cl₂/acetone

(2:2:1 v:v:v) as eluant. Reduction in solvent volume in vacuo and

addition of further hexane resulted in precipitation of the product as

an orange-red solid: yield:1.71 g (32%). ¹H NMR (CDCl₃): δ 1.61 (br,

1H, CH₂), 2.25 (br, 1H, CH₂), 2.60 (br, 2H, CH₂), 4.64 (s, 5H, Cp),

7.22 ꢀ 7.71 (m, 20H, Ph). ³¹P{¹H} NMR (CDCl₃): δ 92.3 (d, J_PP= 38.9

Hz, dppe), 66.9 (d, J_PP= 38.9 Hz, dppe). IR (CH₂Cl₂): ν(CtO)

1847 cm^ꢀ1. MALDI-MS (m/z): 624, [M]⁺; 596 [(M ꢀ CO)]⁺. Anal.

Calcd (%) for C₃₂H₂₉OMoClP₂: C, 61.7; H, 4.7. Found: C, 61.6; H, 4.2.

Preparation of [MoCl(CO)(dppe)Cp*] (1b). Complex 1b was pre-

pared by an identical procedure to that described for 1a from

[MoCl(CO)₃Cp*] (2.88 g, 8.21 mmol) and dppe (4.57 g, 11.49 mmol)

except that, after the initial addition of reagents, reflux was continued for

18 h. The product was obtained as an orange-red solid: yield 1.97 g

(35%). ¹H NMR (CDCl₃): δ 1.33 (s, 15H, Cp*), 1.89 (br, 2H, CH₂),

2.18 (br, 1H, CH₂), 2.62 (br, 1H, CH₂), 7.00ꢀ7.62 (m, 20H, Ph).

1

yellow solid: yield 0.15 g (27%). H NMR (CDCl₃): δ 1.77 (m, 1H,

CH₂), 2.17 (m, 1H, CH₂), 2.42 (m, 2H, CH₂), 4.40 (s, 5H, Cp), 6.56 (d,

2H (AB), J_HH≈ 8.0 Hz, CtCC₆H₅), 6.80 (m, 1H, CtCC₆H₅), 6.90

(m, 2H, CtCC₆H₅), 7.16ꢀ7.82 (m, 20H, Ph, dppe). ³¹P{¹H} NMR

(CDCl₃): δ 89.6 (d, J_PP= 39 Hz, dppe), 78.3 (d, J_PP= 39 Hz, dppe). IR

(CH₂Cl₂): ν(CtC) 2074 cm^ꢀ1, ν(CtO) 1850 cm^ꢀ1. MALDI-MS

(m/z): 663 [(M ꢀ CO)]⁺. Anal. Calcd (%) for C₄₀H₃₄OMoP₂: C, 69.8;

H, 4.9. Found: C, 69.1; H, 4.8.

Preparation of [Mo(CtCPh)(CO)(dppe)Cp*] (5b). Complex 5b was

prepared by an identical procedure to that described for 5a from

[MoCl(CO)(dppe)Cp*] (0.50 g, 0.72 mmol), HCtCPh (0.37 g, 3.61

mmol), and KOBu^t(0.40 g, 3.60 mmol). The product was isolated as a

yellow solid: yield 0.12 g (22%). ¹H NMR: δ 1.42 (s, 15H, C₅Me₅), 1.86

(br, 2H, CH₂), 2.08 (br, 2H, CH₂), 6.38 (d, 2H (AB), J_HH≈ 8 Hz,

C₆H₅), 6.78 (m, 1H, C₆H₅), 6.89 (m, 2H, C₆H₅), 7.15ꢀ7.76 (m, 20H,

Ph, dppe). ³¹P{¹H} NMR (CDCl₃): δ 86.10 (d, J_PP= 37 Hz, dppe), 77.2

(d, J_PP= 36 Hz, dppe). IR (CH₂Cl₂): ν(CtC) 2065, ν(CtO)

³¹P{¹H} NMR (CDCl₃): δ 88.2 (d, J_PP= 32.4 Hz, dppe), 65.2 (d, J_PP

=

32.4 Hz, dppe). IR (CH₂Cl₂): ν(CtO) 1822 cm^ꢀ1. MALDI-MS

(m/z): 666 [(M ꢀ CO)]⁺. Anal. Calcd (%) for C₃₇H₃₉OMoClP₂: C,

64.2; H, 5.6. Found: C, 64.6; H, 5.3.

3775

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

1828 cm^ꢀ1. ES-MS (m/z): 760, [M]⁺. Anal. Calcd (%) for C₄₅H₄₄OMoP₂:

C, 71.2; H, 5.8. Found: C, 70.8; H, 6.3.

ꢀ20 °C gave the product as a yellow solid: yield 0.43 g (29%). ¹H NMR

(CDCl₃): δ 1.51 (m, 18H, PMe₃), 4.92 (s, 5H, Cp), 6.96 (m, 1H, Ph_p),

7.06ꢀ7.19 (m, 4H, Ph_oand Ph_m). ³¹P{¹H} NMR (CDCl₃): δ 25.6 (s,

PMe₃). IR (CH₂Cl₂): ν(CtC) 2056, ν(CtO) 1779 cm^ꢀ1. ES-MS (m/

z): 444 [M]⁺, 416 [(M ꢀ CO)]⁺. Anal. Calcd (%) for C₂₀H₂₈OMoP₂:

C, 54.3; H, 6.3. Found: C, 54.4; H, 6.5.

Preparation of [Mo(CtCC₆H₄-4-Me)(CO)(dppe)Cp] (6a). Complex

6a was prepared by an identical procedure to that described for 5a from

[MoCl(CO)(dppe)Cp] (0.50 g, 0.80 mmol), HCtCC₆H₄-4-Me (0.56

g, 4.83 mmol), and NaOMe (0.50 g, 9.3 mmol). The product was

isolated as a yellow solid: yield 0.11 g (20%). ¹H NMR: δ 1.78 (m, 1H,

CH₂), 2.13 (s, 3H, C₆H₄-4-CH₃), 2.15 (br, 1H, CH₂), 2.36 (m, 2H,

CH₂), 4.40 (s, 5H, Cp), 6.46 (d, 2H (AB), J_HH≈ 8.0 Hz, C₆H₄-4-Me),

6.72 (d, 2H (AB), J_HH≈ 8 Hz, C₆H₄-4-Me), 7.19ꢀ7.83 (m, 20H, Ph).

³¹P{¹H} NMR (CDCl₃): δ 89.7 (d, J_PP= 39 Hz, dppe), 78.1 (d, J_PP= 39

Hz, dppe). IR (CH₂Cl₂): ν(CtC) 2075, ν(CtO) 1848 cm^ꢀ1. MAL-

DI-MS (m/z): 676 [(M ꢀ CO)]⁺. HR ES+-MS (m/z): 704.1295

(C₄₁H₃₆OMoP₂requires 704.1290).

Preparation of [Mo(CtCC₆H₄-4-Me)(CO)(dppe)Cp*] (6b). Com-

plex 6b was prepared by an identical procedure to that described for 5a

from [MoCl(CO)(dppe)Cp*] (0.25 g, 0.36 mmol), HCtCC₆H₄-4-Me

(0.25 g, 2.12 mmol), and KOBu^t(0.24 g, 2.12 mmol). The product was

isolated as a yellow solid: yield 0.053 g (19%). ¹H NMR: δ 1.42 (s, 15H,

C₅Me₅), 1.87 (br, 2H, CH₂), 2.10 (br, 2H, CH₂), 2.13 (s, 3H, C₆H₄-4-

CH₃), 6.31 (d, 2H (AB), J_HH≈ 8.0 Hz, C₆H₄-4-Me), 6.72 (d, 2H (AB),

J_HH≈ 8 Hz, C₆H₄-4-Me), 7.26ꢀ7.76 (m, 20H, Ph). ³¹P{¹H} NMR

(CDCl₃): δ 86.4 (d, J_PP= 36 Hz, dppe), 77.1 (d, J_PP= 36 Hz, dppe). IR

(CH₂Cl₂): ν(CtC) 2068, ν(CtO) 1828 cm^ꢀ1. MALDI-MS (m/z):

746 [(M ꢀ CO)]⁺. Anal. Calcd (%) for C₄₆H₄₆OMoP₂: C, 71.5; H, 6.0.

Found: C, 71.8; H, 5.6.

Preparation of [Mo(CtCPh)(CO)(PMe₃)₂Cp*] (8b). Complex 8b

was prepared by an identical procedure to that described for 8a starting

from [Mo(CtCPh)(CO)₂(PMe₃)Cp*] (0.50 g, 1.07 mmol) and PMe₃

(2.2 cm³of a 1.0 M solution in toluene, 2.2 mmol). The product was

isolated as a yellow solid: yield 0.13 g (24%). ¹H NMR (CDCl₃): δ 1.42

(m, 18H, PMe₃), 1.89 (s, 15H, Cp*), 6.98 (m, 1H, Ph_p), 7.10ꢀ7.22 (m,

4H, Ph_oand Ph_m). ³¹P{¹H} NMR (CDCl₃): δ 23.2 (s, PMe₃). IR

(CH₂Cl₂): ν(CtC) 2056, ν(CtO) 1776 cm^ꢀ1. EI-MS (m/z): 514

[M]⁺, 410 [(M ꢀ CO ꢀ PMe₃)]⁺, 334 [(M ꢀ CO ꢀ 2PMe₃)]⁺. Anal.

Calcd (%) for C₂₅H₃₈OMoP₂: C, 58.6; H, 7.4. Found: C, 58.6; H, 8.1.

Preparation of [Mo(CtCC₆H₄-4-Me)(CO)(PMe₃)₂Cp*] (9b). Com-

plex 9b was prepared by an identical procedure to that described

for 8a starting from [Mo(CtCC₆H₄-4-Me)(CO)₂(PMe₃)Cp*]

(IR (CH₂Cl₂) ν(CtC) 2079, ν(CtO) 1936, 1849 cm^ꢀ1), which

was obtained from the precursor [Mo(CtCC₆H₄-4-Me)(CO)₃Cp*]

(IR (CH₂Cl₂) ν(CtC) 2094, ν(CtO) 2028, 1949, 1989(sh) cm^ꢀ1).

A mixture of [Mo(CtCC₆H₄-4-Me)(CO)₂(PMe₃)Cp*] (1.50 g, 3.14

mmol) and PMe₃(9.42 cm³of a 1.0 M solution in toluene, 9.42 mmol)

was irradiated in a photochemical reactor for 3 h to give an orange-brown

solution, which was evaporated to dryness. The residue, dissolved in

n-hexane, was transferred to an n-hexane-alumina column followed by

elution with hexane/CH₂Cl₂(4:1, v:v). The product was isolated as a

yellow solid: yield 0.52 g (32%). ¹H NMR (CDCl₃): δ 1.37 (m, 18H,

PMe₃), 1.81 (s, 15H, Cp*), 2.21 (s, 3H, C₆H₄-4-CH₃), 7.05 (d, 2H

(AB), J_HH≈ 8.0 Hz, C₆H₄-4-Me), 7.33 (d, 2H (AB), J_HH≈ 8 Hz, C₆H₄-

4-Me). ³¹P{¹H} NMR (CDCl₃): δ 23.2 (s, PMe₃). IR (CH₂Cl₂):

ν(CtC) 2057, ν(CtO) 1770 cm^ꢀ1. EI-MS (m/z): 528 [M]⁺. Anal.

Calcd (%) for C₂₆H₄₀OMoP₂: C, 59.3; H, 7.6. Found: C, 59.4; H, 7.8.

Electronic Structure Calculations. All calculations were carried

out using the Gaussian 03 package.³⁶The model geometries for 5-H and

8-H were optimized using the B3LYP functional,³⁷with no symmetry

constraints. The Def2-SVP basis, obtained from the Turbomole

library,³⁸was used for all atoms. Frequency calculations were carried

out on these optimized geometries at the corresponding levels and

shown to have no imaginary frequencies. Molecular orbital computa-

tions were carried out on these optimized geometries, and the orbital

contributions were generated with the aid of GaussSum.³⁹

Preparation of [Mo(CtCPh)(CO)₂(PMe₃)Cp] (7a). A mixture of

[Mo(CtCPh)(CO)₃Cp] (2.15 g, 6.22 mmol), PMe₃(18.7 cm³of a

1.0 M solution in toluene, 18.7 mmol), and Me₃NO 2H₂O (1.38 g,

3

12.43 mmol) in NCMe (50 cm³) was stirred at room temperature for

0.5 h to give an orange-brown solution, which was evaporated to dryness.

The residue, dissolved in CH₂Cl₂, was transferred to an n-hexane-

alumina column, and the product eluted as a yellow band with hexane/

CH₂Cl₂(1:1 v:v) as eluant. Recrystallization from pentane at ꢀ20 °C

gave the product as a yellow solid: yield 1.34 g (55%). ¹H NMR

(CDCl₃): δ 1.55 (d, 9H, J_HP= 9.2 Hz, PMe₃), 5.26 (s, 5H, Cp), 7.01 (m,

1H, Ph_p), 7.15 (m, 4H), Ph_oand Ph_m. ³¹P{¹H} NMR (CDCl₃): δ 15.8

(s, PMe₃). IR (CH₂Cl₂): ν(CtC) 2083, ν(CtO) 1956, 1863 cm^ꢀ1. EI-

MS (m/z): 396 [M]⁺, 368 [(M ꢀ CO)]⁺, 340 [(M ꢀ 2CO)]⁺, 322

[(M ꢀ PMe₃)]⁺. Anal. Calcd (%) for C₁₈H₁₉O₂MoP: C, 54.8; H, 4.8.

Found: C, 54.6; H, 4.6.

Preparation of [Mo(CtCPh)(CO)₂(PMe₃)Cp*] (7b). Complex 7b

was prepared by an identical procedure to that described for 7a from

[Mo(CtCPh)(CO)₃Cp*] (2.60 g, 6.25 mmol), PMe₃(18.8 cm³of a

Crystallography. The majority of details of the structure analyses

carried out on complexes 5b, 6a, 6b, 7b, 8a, 8b, and 9b are given in

Table 11. Single crystals of the complexes were obtained as follows: 5b,

6a/b, and 9b: vapor diffusion of n-pentane into a toluene solution of the

complex to give yellow needles; 8a/b and 9b: solution of n-pentane at

ꢀ20 °C; 7b: vapor diffusion of n-pentane into a CH₂Cl₂solution of the

complex to give yellow needles. X-ray data for all seven complexes were

collected with an Oxford Diffraction X-Calibur 2 diffractometer

equipped with an Oxford-Cryosystems low-temperature device at

100(2) K by means of Mo KR radiation and ω scans. Data were

corrected for Lorenz and polarization factors, and absorption correc-

tions were applied to all data. Structures were solved by direct methods

with refinement by full-matrix least-squares based on F²against all

reflections. Cell refinement and data reduction were carried out with

CrysAlis CCD and CrysAlis RED software (Oxford Diffraction Ltd.).

SHELXS-97⁴⁰was employed for computing the structure solution and

SHELXL-97⁴¹for computing structure refinement. Difference Fourier

syntheses were employed in positioning idealized H atoms, which were

allowed to ride on their parent C atoms. All non-H atoms were refined

anisotropically, and H atoms were included in calculated positions.

C(10) and C(14)ꢀC(18) of the Cp* ring in structure 7b were

1.0 M solution in toluene, 18.8 mmol), and Me₃NO 2H₂O (1.39 g,

3

12.50 mmol). The product was isolated as a yellow solid: yield 1.78 g

1

(62%). H NMR (CDCl₃): δ 1.53 (d, 9H, J_HP= 9.2 Hz, PMe₃), 2.03

(s, 15H, Cp*), 7.12 (m, 1H, Ph_p), 7.24 (m, 2H), 7.31 (m, 2H), Ph_oand Ph_m.

³¹P{¹H} NMR (CDCl₃): δ 10.8 (s, PMe₃). IR (CH₂Cl₂): ν(CtC) 2078,

ν(CtO) 1938, 1851 cm^ꢀ1. EI-MS (m/z): 466 [M]⁺, 438 [(M ꢀ CO)]⁺,

410 [(M ꢀ 2CO)]⁺, 390 [(M ꢀ PMe₃)]⁺, 390 [(M ꢀ 2CO ꢀ PMe₃)]⁺.

HR ES+-MS (m/z): 466.0946 (C₂₃H₂₉O₂MoP requires 466.0954). Anal.

Calcd (%) for C₂₃H₂₉O₂MoP: C, 59.5; H, 6.3. Found: C, 59.2; H, 5.8.

Preparation of [Mo(CtCPh)(CO)(PMe₃)₂Cp] (8a). A mixture of

[Mo(CtCPh)(CO)₂(PMe₃)Cp] (1.34 g, 3.41 mmol) and PMe₃

(6.8 cm³of a 1.0 M solution in toluene, 6.8 mmol) in toluene

(80 cm³) was irradiated in a photochemical reactor (Hanovia, 125 W)

for 3 h to give an orange-brown solution, which was evaporated to

dryness. The residue, dissolved in n-hexane, was transferred to an n-

hexane-alumina column, and two bands were eluted with hexane/

CH₂Cl₂(4:1, v:v) as eluant. The first band was identified as the product

8a by IR spectroscopy; the second band was identified by IR spectros-

copy as starting material, 7a. Complex 8a was collected as the first band

from the column and solvent removed. Recrystallization from pentane at

3776

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

Table 11. Crystal Data and Reﬁnement Parameters

5b

6a

6b

7b

8a

8b

9b

formula

mass

C

758.68

₄₅H₄₄MoOP₂

C₄₁H₃₆MoOP₂

702.58

C₄₆H₄₆MoOP₂

772.71

C₂₃H₂₉MoO₂P

464.37

C₂₀H₂₈MoOP₂

442.30

C₂₅H₃₈MoOP₂

512.43

C₂₆H₄₀MoOP₂

526.46

λ (Å)

0.71069

monoclinic

P 21/n

9.9199 (3)

21.3484(7)

17.4064(6)

90

0.71073

monoclinic

P 21/c

0.71069

monoclinic

P 21/c

0.71073

monoclinic

P 21/c

0.71073

orthorhombic

Pbca

0.71069

triclinic

0.71069

triclinic

cryst syst

space group

a (Å)

P-1

12.3460(4)

16.4490(5)

16.0400(6)

90

17.151(5)

12.436(5)

18.564(5)

90

17.910(3)

8.1224(7)

16.471(2)

90

14.749(4)

8.9958(5)

31.027(2)

90

12.6102(4)

13.4489(5)

16.0881(5)

109.493(3)

100.261(3)

90.310(3)

2524.7(1); 4

0.660

13.1792(4)

13.6485(4)

15.4833(4)

73.776(3)

80.141(3)

82.039(3)

2622.6(1); 4

0.637

b (Å)

c (Å)

R (deg)

β (deg)

102.170(4)

90

97.2200(12)

90

108.536(5)

90

114.180(17)

90

γ (deg)

90

V (Å³); Z

absorp coeﬀ (mm^ꢀ1

θ range (deg)

3603.4(2); 4

0.488

3231.56(19); 4

0.538

3754(2); 4

0.470

2185.9(5); 4

0.688

4167(1); 8

0.797

)

2.90ꢀ28.66

ꢀ13, 12

ꢀ26, 28

ꢀ23, 9

1.66ꢀ25.85

0, 15

2.82ꢀ26.37

ꢀ21, 18

ꢀ13, 15

ꢀ23, 19

7557

2.85ꢀ28.37

ꢀ22, 18

ꢀ10, 6

ꢀ18, 21

4839

2.73ꢀ28.37

ꢀ18, 12

ꢀ11, 10

ꢀ27, 41

4563

2.91ꢀ28.56

ꢀ15, 11

ꢀ17, 17

ꢀ20, 17

11 062

2.99ꢀ28.64

ꢀ17, 17

ꢀ14, 18

ꢀ19, 20

11 622

limiting indices (h,k,l)

0, 20

ꢀ19, 19

6130

total reﬂns

8203

indep reﬂns, I > 2σ(I)

5313

3836

4750

3221

3396

6462

8662

R₁

0.0350

0.0782

0.0511

0.0450

0.0685

0.1339

88.9

0.0301

0.0298

wR₂

0.0664

0.1862

0.0834

0.1178

0.0524

0.0657

data completeness

88.4

98.1

98.3

88.6

86.1

86.3

disordered and therefore constrained and split into parts. Structures 8b

and 9b contained two molecules in the asymmetric unit.

16, 5988. (d) Le Narvor, N.; Toupet, L.; Lapinte, C. J. Am. Chem. Soc.

1995, 117, 7129.

(4) (a) Fox, M. A.; Roberts, R. L.; Khairul, W. M.; Hartl, F.; Low, P. J.

J. Organomet. Chem. 2007, 692, 3277. (b) Bruce, M. I.; Low, P. J.;

Costuas, K.; Halet, J.-F.; Best, S. P.; Heath, G. A. J. Am. Chem. Soc. 2000,

122, 1949.

(5) (a) Paul, F.; Ellis, B. G.; Bruce, M. I.; Toupet, L.; Roisnel, T.;

Costuas, K.; Halet, J.-F.; Lapinte, C. Organometallics 2006, 25, 649.

(b) Bruce, M. I.; Ellis, B. G.; Low, P. J.; Skelton, B. W.; White, A. H.

Organometallics 2003, 22, 3184.

(6) (a) Ramsden., J. A.; Weng, W.; Gladysz, J. A. Organometallics

1992, 11, 3635. (b) Weng, W.; Bartik, T.; Brady, M.; Bartik, B.;

Ramsden, J. A.; Arif, A. M.; Gladysz, J. A. J. Am. Chem. Soc. 1995,

117, 11922. (c) Brady, M.; Weng, W.; Zhou, Y.; Seyler, J. W.; Amoroso,

A. J.; Arif, A. M.; B€ohme, M.; Frenking, G.; Gladysz, J. A. J. Am. Chem.

Soc. 1997, 119, 775.

’ ASSOCIATED CONTENT

S

Supporting Information. Cyclic voltammograms of 6b

b

and 9b showing E_p(A) (irreversible), IR spectroelectrochemistry

for [5b]ⁿ⁺, [6b]ⁿ⁺, and [9b]ⁿ⁺, UVꢀvisible spectroelectrochemistry

for [5b]ⁿ⁺, selected EPR spectra for [3a]⁺, [4b]⁺, [8b]⁺, [1a]⁺,

[1b]⁺, [6a]⁺, and [6b]⁺, and CIF ﬁles giving crystallographic data

for complexes 5b, 6a, 6b, 7b, 8a, 8b, and 9b. This material is

available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION

(7) (a) Brown, N. J.; Collison, D; Edge, R.; Fitzgerald, E. C.;

Helliwell, M.; Howard, J. A. K.; Lancashire, H. N.; Low, P. J.; McDouall,

J. J. W.; Raftery, J.; Smith, C. A.; Yuﬁt, D. S.; Whiteley, M. W.

Organometallics 2010, 29, 1261. (b) Brown, N. J.; Collison, D.; Edge,

R.; Fitzgerald, E. C.; Low, P. J.; Helliwell, M.; Ta, Y. T.; Whiteley, M. W.

Chem. Commun. 2010, 46, 2253.

Corresponding Authors

*E-mail: p.j.low@durham.ac.uk; Mark.Whiteley@manchester.

ac.uk.

(8) Lancashire, H. N.; Brown, N. J.; Carthy, L.; Collison, D.;

Fitzgerald, E. C.; Edge, R.; Helliwell, M.; Holden, M; Low, P. J.;

McDouall, J. J. W.; Whiteley, M. W. Dalton Trans. 2011, 40, 1267.

(9) St€arker, K; Curtis, M. D. Inorg. Chem. 1985, 24, 3006.

(10) Fettinger, J. C.; Keogh, D. W.; Poli, R. J. Am. Chem. Soc. 1996,

118, 3617.

’ ACKNOWLEDGMENT

We thank the EPSRC for support of this work through grants

EP/E025544/1 and EP/E02582X/1 and the Nuﬃeld Founda-

tion for the award of an Undergraduate Research Bursary to R.L.

(URB/37028). P.J.L. holds an EPSRC Leadership Fellowship.

(11) Moreno, C.; Gꢀomez, J. L.; Medina, R.-M.; Macazaga, M.-J.;

Arnanz, A.; Lough, A.; Farrar, D. H.; Delgado, S. J. Organomet. Chem.

1999, 579, 63.

’ REFERENCES

(12) Treichel, P. M.; Barnett, K. W.; Shubkin, R. L. J. Organomet.

Chem. 1967, 7, 449.

(13) Filippou, A. C.; Winter, J. G.; Kociok-K€ohn, G.; Troll, C.; Hinz,

I. Organometallics 1999, 18, 2649.

(14) Nickias, P. N.; Selegue, J. P.; Young, B. A. Organometallics 1988,

7, 2248.

(1) Low, P. J.; Bruce, M. I. Adv. Organomet. Chem. 2001, 48, 71.

(2) Bruce, M. I.; Low, P. J. Adv. Organomet. Chem. 2004, 50, 179.

(3) (a) Denis, R.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics

2000, 19, 4240. (b) Paul, F.; Toupet, L.; Thꢀepot, J.-Y.; Costuas, K.;

Halet, J.-F.; Lapinte, C. Organometallics 2005, 24, 5464. (c) Coat, F.;

Guillevic, M.-A.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics 1997,

3777

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Organometallics

ARTICLE

(15) Connelly, N. G.; Geiger, W. E.; Lagunas, M. C.; Metz, B.;

Rieger, A. L.; Rieger, P. H.; Shaw, M. J. J. Am. Chem. Soc. 1995,

117, 12202.

(38) Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R. Theor.

Chem. Acc. 1997, 97, 119.

(39) O’Boyle, N. M.; Tenderholt, A. L.; Langer, K. M. J. Comput.

Chem. 2008, 29, 839.

(16) Yang, J.-Y.; Huang, S.-L.; Lin, Y.-C.; Liu, Y.-H.; Wang, Y.

Organometallics 2000, 19, 269.

(17) Adams, H.; Atkinson, M. T.; Morris, M. J. J. Organomet. Chem.

2001, 633, 125.

(18) Bruce, M. I.; Ke, M.; Low, P. J.; Skelton, B. W.; White, A. H.

Organometallics 1998, 17, 3539.

(40) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure

Solution; Universit€at G€ottingen: Germany, 1997.

(41) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure

Reﬁnement; Universit€at G€ottingen: Germany, 1997.

(19) Pombeiro, A. J. L.; Hills, A.; Hughes, D. L.; Richards, R. L.

J. Organomet. Chem. 1990, 398, C15.

(20) Gamasa, M. P.; Gimeno, J.; Zhang, L.; Lanfranchi, M.;

Tiripicchio, A. J. Organomet. Chem. 1996, 514, 287.

(21) Bush, M. A.; Hardy, A. D. U.; Manojlovic-Muir, Lj.; Sim, G. A.

J. Chem. Soc. (A) 1971, 1003.

(22) Poli, R. Organometallics 1990, 9, 1892.

(23) Lin, Z.; Hall, M. B. Organometallics 1993, 12, 19.

(24) Abugideiri, F.; Fettinger, J. C.; Keogh, W.; Poli, R. Organome-

tallics 1996, 15, 4407.

(25) Denisovich, L. I.; Filatova, T. V.; Peterleitner, M. G.; Ustynyuk,

N. A.; Vinogradova, V. N.; Leont'eva, L. I. Russ. Chem. Bull. 1998,

47, 1901.

(26) Lau, Y. Y.; Huckabee, W. W.; Gipson, S. L. Inorg. Chim. Acta

1990, 172, 41.

(27) (a) Krejeik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. 1991,

317, 179. (b) Spectroelectrochemistry; Kaim, W.; Klein, A., Eds.; Royal

Society of Chemistry: Cambridge, 2008.

(28) Bruce, M. I.; Low, P. J.; Hartl, F.; Humphrey, P. A.; de

Montigny, F.; Jevric, M.; Lapinte, C.; Perkins, G. J.; Roberts, R. L.;

Skelton, B. W.; White, A. H. Organometallics 2005, 24, 5241.

(29) Fox, M. A.; LeGuennic, B.; Roberts, R. L.; Baines, T. E.; Yuﬁt,

D. S.; Albesa-Jovꢀe, D.; Halet, J.-F.; Hartl, F.; Howard, J. A. K.; Low, P. J.

J. Am. Chem. Soc. 2008, 130, 3566.

(30) Maurer, J.; Linseis, M.; Sarkar, B.; Schwederski, B.; Niemer, M.;

Kaim, W.; Zalis, S.; Anson, C.; Zabel, M.; Winter, R. F. J. Am. Chem. Soc.

2008, 130, 259.

(31) Aston, G. M.; Badriya, S.; Farley, R. D.; Grime, R. W.; Ledger,

S. J.; Mabbs, F. E.; McInnes, E. J. L.; Morris, H. W.; Ricalton, A.;

Rowlands, C. C.; Wagner, K.; Whiteley, M. W. J. Chem. Soc., Dalton

Trans. 1999, 4379.

(32) Green, M. L. H.; Knight, J.; Segal, J. A. J. Chem. Soc., Dalton

Trans. 1977, 2189.

(33) Kubꢀaꢁcek, P.; Hoﬀmann, R.; Havias, Z. Organometallics 1982,

1, 180.

(34) (a) Kubas, G. J.; Kiss, G.; Hoﬀ, C. D. Organometallics 1991,

10, 2870. (b) Asdar, A.; Tudoret, M.-J.; Lapinte, C. J. Organomet. Chem.

1988, 349, 353.

(35) (a) Bruce, M. I.; Humphrey, M. G.; Matisons, J. G.; Roy, S. K.;

Swincer, A. G. Aust. J. Chem. 1984, 37, 1955. (b) Biradar, A. V.; Dongare,

M. K.; Umbarkar, S. B. Tetrahedron Lett. 2009, 50, 2885.

(36) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,

K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;

Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;

Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,

J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,

X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;

Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;

Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;

Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,

S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;

Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;

Cliﬀord, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,

P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;

Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,

B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.Gaussian 03,

Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.

(37) Becke, A. D. J. Chem. Phys. 1993, 98, 648.

3778

dx.doi.org/10.1021/om200229c |Organometallics 2011, 30, 3763–3778

Article Doi

Synthesis, redox chemistry, and electronic structure of the alkynyl cyclopentadienyl molybdenum complexes [Mo(C≡CR)(CO)(L2)Cp] n+ (n = 0 or 1; R = Ph or C6H4-4-Me, L 2 = Ph2PCH2C

DOI: 10.1021/om200229c

Source and publish data:

Authors:

Article abstract of DOI:10.1021/om200229c

Full text of DOI:10.1021/om200229c

Products guided by the article

R&D Labs maybe for 176507-40-7

Relevant to this article

Hot Product