Air-stable fluorescent primary phosphine complexes of molybdenum and tungsten

Article abstract of DOI:10.1080/00958972.2016.1193169

Here we report a study on the reactivity of the fluorescent air-stable primary phosphine 8-((4-phosphino)phenyl)-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene 4 with [Mo(CO)₆], [W(CO)₆], [Mo(CO)₄

Full text of DOI:10.1080/00958972.2016.1193169

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Air-stable fluorescent primary phosphine
complexes of molybdenum and tungsten
Laura H. Davies, Jennifer F. Wallis, Ross W. Harrington, Paul G. Waddell & Lee
J. Higham
To cite this article: Laura H. Davies, Jennifer F. Wallis, Ross W. Harrington, Paul G. Waddell &
Lee J. Higham (2016): Air-stable fluorescent primary phosphine complexes of molybdenum and
tungsten, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2016.1193169
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1193169
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Date: 05 June 2016, At: 20:27

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2016.1193169
Air-stable fluorescent primary phosphine complexes of
molybdenum and tungsten
LAURA H. DAVIES, JENNIFER F. WALLIS, ROSS W. HARRINGTON, PAUL G. WADDELL
and LEE J. HIGHAM*
School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
Here we report a study on the reactivity of the fluorescent air-stable primary phosphine 8-((4-phosphino)phenyl)-4,4-
dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene 4 with [Mo(CO)6], [W(CO)6],
[Mo(CO)4(piperidine)] and [W(CO)4(piperidine)] which yields the mono-phosphine [Mo(CO)5(4)] 5, [W(CO)5(4)] 6
and di-phosphine cis-[Mo(CO)4(4)2] (7) and cis-[W(CO)4(4)2] (9) complexes as the predominant products. In
addition to the characterisation of these complexes by multinuclear NMR and IR spectroscopy, and mass
spectrometry, the solid state structures of 6 and cis-7 have also been determined by single crystal X-ray diffraction.
The photophysical properties of the complexes show that the incorporation of the phosphorus ligand has a limited
effect on the absorption and emission profile of the Bodipy core and that they retain similar quantum yields to their
parent Bodipy dyes. Small quantities of the by-products trans-[Mo(CO)4(4)2] (7), cis-[Mo(CO)4(piperidine)(4)] (8)
and cis-[W(CO)4(piperidine)(4)] (10) were also isolated and characterized.
Keywords: Air-stability; Bodipy; Fluorescence; Molybdenum; Primary phosphines; Tungsten
1. Introduction
Primary phosphines are widely regarded as difficult to handle and have a reputation for toxicity, volatility, and
spontaneous inflammability [1]. Their use has therefore been somewhat limited despite the fact they are versatile
starting materials with two reactive P–H bonds. Primary phosphines and their derivatives have found applications in
medicinal chemistry [2], polymer science [3], carbohydrate functionalization [4], macrocycle synthesis [5] and
catalysis [6]. However we have recently developed a working model based on Density Functional Theory which
indicates that contrary to popular belief, many primary phosphines will be air-stable if the molecule contains the
appropriate degree of π-conjugation or heteroatoms - a stabilizing feature quite separate from the known
phenomenon of steric hindrance [7]. This model helped us to rationalize our preparation of the first air-stable chiral
primary phosphines [8] and predicted that incorporation of the phosphino group onto the highly conjugated boron
dipyrromethene (Bodipy) skeleton would result in a similar resistance to air oxidation. We have since prepared the
first air-stable fluorescent primary phosphines [9], and used them to synthesize tridentate tertiary phosphine ligands
that complex rhenium and technetium, which we have then exploited in biological cell imaging [10]. Despite the
extensive coordination studies of tertiary phosphines to transition metals, the corresponding studies of primary
phosphines remains relatively scarce [11], and the coordination of fluorescent primary phosphine has not yet been
reported, notwithstanding a preliminary short report of ours [12]. Of particular interest to us are the group six metal
complexes, which are routinely prepared with tertiary phosphines to gain a greater understanding of their electronic
properties [13]. Here we report molybdenum and tungsten complexes of the most fluorescent primary phosphine we
have prepared to date, and describe their somewhat surprising photophysical properties.
*Corresponding author. Email: lee.higham@ncl.ac.uk
1

2. Experimental
2.1. General procedure
All air- and/or water-sensitive reactions were performed under a nitrogen atmosphere using standard Schlenk line
techniques. Tetrahydrofuran and toluene were dried over sodium/benzophenone and sodium, respectively, and
dichloromethane was dried over calcium hydride - these solvents were distilled prior to use. Solvents used for
column chromatography were not anhydrous. All starting materials were purchased from Aldrich, Acros Organics,
Alfa Aesar or Strem and used as received. The primary phosphine 8-((4-phosphino)phenyl)-4,4-dimethyl-1,3,5,7-
tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene 4 [14], cis-[Mo(CO)4(pip)2] [13a] and cis-[W(CO)4(pip)2] [15]
were prepared according to literature procedures.Flash chromatography was performed on silica gel from
Fluorochem (silica gel, 40-63u, 60A). Thin-layer chromatography was carried out on Fisher aluminium-based plates
with silica gel and fluorescent indicator (254 nm). 1H, 13C{1H}, 31P{1H}, 31P-1H, and 11B{1H} NMR spectra were
recorded on a JEOL Lambda 500 (1H 500.16 MHz), JEOL ECS-400 (1H 399.78 MHz) or Bruker Avance III 300 (1H
300.13 Hz) spectrometer at room temperature (21°C); 1H and 13C shifts are reported relative to tetramethylsilane, 31
relative to 80% H3PO4 and 11B relative to BF3.Et2O. Infrared spectra were recorded on a Varian 800 FT-IR
spectrometer and mass spectrometry was carried out by the EPSRC National Mass Spectrometry Service Centre,
Swansea.
P
2.2. Synthesis of the mono-substituted complexes
2.2.1. [Mo(CO)5(4)] 5. A solution of [Mo(CO)6] (0.066 g, 0.25 mmol) in anhydrous THF (15 mL) was irradiated
with UV light in a quartz vessel under a stream of nitrogen at room temperature for one hour. Primary phosphine 4
(0.100 g, 0.25) in anhydrous THF (15 mL) was added and the mixture was irradiated for a further two hours. The
solvent was removed and the red product was purified by column chromatography (hexane:chloroform 4:1), to yield
the intended product as an orange solid (0.041 g, 26%). 1H NMR (300 MHz, CDCl3) δ 7.66 (m, 2H), 7.42 (m, 2H),
5.56 (d, 1JHP = 326.7 Hz, 2H), 2.45 (s, 6H), 2.31 (q, J = 7.5 Hz, 4H), 1.25 (s, 6H), 0.99 (t, J = 7.5 Hz, 6H), 0.28 (s,
6H) ppm; 13C{1H} NMR (75 MHz, CDCl3) δ 208.8 (d, 2JCP = 24.2 Hz), 204.7 (d, 2JCP = 9.8 Hz), 151.2, 139.9, 138.7,
133.6, 132.9, 132.7 (d, JCP = 11.7 Hz), 130.0 (d, JCP = 10.6 Hz), 128.8, 126.8 (d, 1JCP = 42.3 Hz), 17.6, 14.8, 14.5,
12.1, 10.4 (br) ppm; 31P-1H NMR (121 MHz, CDCl3) δ −63.5 (tt, 1JPH = 326.7 Hz, 3JPH = 11.8 Hz) ppm; 11B{1H}
NMR (96 MHz, CDCl3) δ −2.2 ppm; IR (neat) ෤ = 2962, 2929, 2868, 2076, 1992, 1929 cm-1; HRMS (APCI+) calcd.
for C30H35B1N2P1O5Mo1 [M + H]+ requires m/z 636.1476, found 636.1493.
2.2.2. [W(CO)5(4)] 6. A solution of [W(CO)6] (0.050 g, 0.14 mmol) in anhydrous THF (15 mL) was irradiated with
UV light in a quartz vessel under a stream of nitrogen at room temperature for one hour. Primary phosphine 4 (0.057
g, 0.14 mmol) in anhydrous THF (15 mL) was added and the mixture was irradiated for a further two hours. The
solvent was evaporated and purified by column chromatography (hexane:chloroform 4:1) which yielded a red solid
(0.018 g, 10%). 1H NMR (300 MHz, CDCl3) δ 7.67 (m, 2H), 7.46 (m, 2H), 5.91 (d, 1JHP = 340.3 Hz, 2H), 2.46 (s,
6H), 2.32 (q, J = 7.6 Hz, 4H), 1.25 (s, 6H), 0.99 (t, J = 7.6 Hz, 6H), 0.29 (s, 6H) ppm; 13C{1H} NMR (75 MHz,
CDCl3) δ 198.3 (d, JCP = 23.1 Hz), 195.5 (d, JCP = 7.2 Hz), 151.3, 140.2, 138.5, 133.6, 132.9, 132.8 (d, JCP =11.3
Hz), 130.1 (d, JCP = 10.5 Hz), 128.8, 126.1 (d, 1JCP = 47.3 Hz), 17.6, 14.8, 14.5, 12.2, 10.5 (br) ppm; 31P-1H NMR
(121 MHz, CDCl3) δ −85.7 (tt, 1JPH = 340.6 Hz, 3JPH = 12.1 Hz, 1JPW = 222.9) ppm; 11B{1H} NMR (96 MHz, CDCl3)
δ −1.6 ppm; IR (neat) ෤ = 2958, 2926, 2869, 2077, 1973, 1902 cm-1; HRMS (APCI+) calcd. for
C30H35N2O5P110B1182W1 (M + H)+ requires m/z 726.1890, found 726.1902.
2.3. Synthesis of the di-substituted complexes
2.3.1. Cis-[Mo(CO)4(4)2] Cis-7. Cis-[Mo(CO)4(pip)2] (0.070 g, 0.19 mmol) and 4 (0.150 g, 0.37 mmol) were
dissolved in anhydrous dichloromethane (6 mL) under nitrogen. The reaction was refluxed for two hours; complete
consumption of the starting material was monitored by 31P NMR spectroscopy. The solvent was evaporated and the
complex purified by column chromatography on silica gel (petroleum ether/dichloromethane 3:1, Rf = 0.5) to yield
an orange solid (0.120 g, 63%). A sample suitable for X-ray crystallographic analysis was obtained from
chloroform/pentane. 1H NMR (500 MHz, CDCl3) δ 7.64 (dd, 3JHH = 7.8 Hz, 3JHP = 11.5 Hz, 4H), 7.26 (dd, 3JHH = 7.8
Hz, 4JHP = 1.4 Hz, 4H), 5.50 (dd, 1JHP = 318.9 Hz, 3JHP = 8.7 Hz, 4H), 2.44 (s, 12H), 2.29 (q, 3JHH = 7.8 Hz, 8H), 1.22
2

(s, 12H), 0.96 (t, 3JHH = 7.8 Hz, 12H), 0.26 (s, 12H) ppm; 13C{1H} NMR (126 MHz, CDCl3) δ 213.1 (dd, CO), 207.8
(pseudo t, 2JCP = 9.4 Hz, CO), 151.1, 139.5, 138.8, 133.5, 133.0, 132.9 (JCP = 7.5 Hz), 129.8, 128.8, 127.3 (m), 17.5,
14.8, 14.4, 12.1, 10.5 (br) ppm; 31P-1H NMR (202 MHz, CDCl3) δ −56.1 (tm, 1JHP = 318.9 Hz) ppm; 11B{1H} NMR
(128 MHz, CDCl3) δ −1.8 ppm; IR (neat): ෤ = 2360, 2332, 2029, 1947, 1919, 1896 cm−1; HRMS (ESI+) calcd. for
C54H69B2N4P2O4Mo1 [M+H]+ requires m/z 1012.4084, found m/z 1012.4078 (0.6 ppm).
2.3.2. Trans-[Mo(CO)4(4)2] Trans-7. The complex was purified by column chromatography on silica gel (petroleum
ether/dichloromethane 3:1, Rf = 0.3) to yield an orange solid (0.021g, 11%). 1H NMR (500 MHz, CDCl3) δ 7.56 (dd,
3
J
HP = 10.5 Hz, 3JHH = 7.8 Hz, 4H), 7.31 (d, 3JHH = 7.8 Hz, 4H), 5.31 (dd, 1JHP = 316.5 Hz, 3JHP = 8.8 Hz, 4H), 2.38
(s, 12H), 2.22 (q, 3JHH = 7.8 Hz, 8H), 1.19 (s, 12H), 0.88 (t, 3JHH = 7.8 Hz, 12H), 0.19 (s, 12H) ppm; 13C{1H} NMR
(126 MHz, CDCl3) δ 216.8 (br, CO), 151.1, 139.1, 138.9, 135.0, 133.5, 133.1 (pseudo t, JCP = 4.8 Hz), 132.8, 129.7
(pseudo t, JCP = 3.8 Hz), 128.9, 17.5, 14.7, 14.4, 12.2, 10.5 (br) ppm; 31P-1H NMR (202 MHz, CDCl3) δ −48.8 (tm,
1
J
PH = 316.5 Hz) ppm; 11B{1H} NMR (128 MHz, CDCl3) δ −1.9 ppm; IR (neat): ෤ = 2312, 2294, 1959, 1868 cm−1;
HRMS (ESI+) calcd. for C54H6910B111B1N4P2O492Mo1 [M+H]+ requires m/z 1012.4084, found m/z 1012.4073 (1.1
ppm).
2.3.3. Cis-[Mo(CO)4(pip)(4)] Cis-8. The complex was purified by column chromatography on silica gel (petroleum
ether/dichloromethane 5:1, Rf = 0.5) to yield an orange solid (0.012 g, 6%). 1H NMR (500 MHz, CDCl3) δ 7.66 (dd,
3
J
J
HP = 11.9 Hz, 3JHH = 7.8 Hz, 2H), 7.42 (d, 3JHH = 7.8 Hz, 2H), 5.56 (d, 1JHP = 327.7 Hz, 2H), 2.45 (s, 6H), 2.30 (q,
HH = 7.3 Hz, 4H), 1.25 (br, 11H), 1.25 (s, 6H), 0.98 (t, 3JHH = 7.3 Hz, 6H), 0.27 (s, 6H) ppm; 31P-1H NMR (202
3
MHz, CDCl3) δ −63.5 (tt, 1JPH = 327.7 Hz, 3JPH = 11.8 Hz) ppm; 11B{1H} NMR (128 MHz, CDCl3) δ −2.1 ppm; IR
(neat): ෤ = 2361, 2340, 2077, 1993, 1951 cm−1; HRMS (ESI+) calcd. for C34H4611B1N3PO497Mo1 [M+H]+ requires
m/z 699.2379, found m/z 699.2392 (1.9 ppm).
2.3.4. Cis-[W(CO)4(4)2] Cis-9. Cis-[W(CO)4(pip)2] (0.057 g, 0.126 mmol) and 4 (0.100 g, 0.247 mmol) were
dissolved in anhydrous toluene (5 mL) under nitrogen and the reaction was heated to 75 °C for 20 hours. The solvent
was evaporated and the complex was purified by column chromatography on silica gel (petroleum
ether/dichloromethane 5:1, Rf = 0.2) to yield an orange solid (0.092 g, 67%). 1H NMR (400 MHz, CDCl3) δ 7.64 (dd,
3
J
HH = 7.9 Hz, 3JHP = 11.8 Hz, 4H), 7.42 (dd, 3JHH = 7.9 Hz, 4JHP = 1.6 Hz, 4H), 5.79 (d, 1JHP = 388.9 Hz, 4H), 2.44
(s, 12H), 2.29 (q, 3JHH = 7.6 Hz, 8H), 1.24 (s, 12H), 0.96 (t, 3JHH = 7.6 Hz, 12H), 0.26 (s, 12H) ppm; 13C{1H} NMR
(100 MHz, CDCl3) δ 203.5 (br dd, CO), 199.3 (pseudo t, 2JCP = 7.3 Hz, CO), 151.2, 139.7, 138.6, 133.4, 132.9
(pseudo t, JCP = 5.7 Hz), 132.7, 129.8 (pseudo t, JCP = 4.3 Hz), 128.7, 126.9, 17.4, 14.7, 14.3, 12.0, 10.4 (br) ppm;
31P-1H NMR (202 MHz, CDCl3) δ −76.9 (t, 1JHP = 388.9 Hz, 1JPW = 217.4 Hz) ppm; 11B{1H} NMR (128 MHz,
CDCl3) δ −2.0 ppm; IR (neat): ෤ = 2961, 2926, 2870, 2359, 2341, 2026, 1940, 1912, 1888 cm−1; HRMS (ESI+) calcd.
for C54H68B2N4P2O4W1 [M]+ requires m/z 1102.4507, found m/z 1102.4486 (1.9 ppm).
2.3.5. Cis-[W(CO)4(pip)(4)] Cis-10. The complex was purified by column chromatography on silica gel (petroleum
ether/dichloromethane 5:1, Rf = 0.4) to yield an orange solid (0.008 g, 9%). 1H NMR (400 MHz, CDCl3) δ 7.65 (dd,
3
J
HH = 8.0 Hz, 3JHP = 12.5 Hz, 2H), 7.44 (dd, 3JHH = 8.0 Hz, 4JHP = 2.2 Hz, 2H), 5.89 (d, 1JHP = 340.8 Hz, 2H), 2.44
(s, 6H), 2.30 (q, 3JHH = 7.5 Hz, 4H), 1.55 (s, 6H), 1.24 (m, 11H), 0.97 (t, 3JHH = 7.5 Hz, 6H), 0.26 (s, 6H) ppm; 31P-
1H NMR (202 MHz, CDCl3) δ −85.0 (tt, 1JPH = 340.8 Hz, 3JPH = 12.0 Hz, 1JPW = 223.2 Hz) ppm; 11B{1H} NMR (128
MHz, CDCl3) δ −1.9 ppm; IR (neat): ෤ = 2954, 2921, 2852, 2361, 2332, 2024, 1986, 1942, 1924 cm−1; HRMS (ESI+)
calcd. for C34H45B1N3P1O4W1 [M]+ requires m/z 783.2838, found m/z 783.2842 (0.5 ppm).
2.4. Absorption and emission spectroscopy
Absorption spectra were recorded on a Hitachi Model U-3310 spectrophotometer while fluorescence studies were
recorded using a Hitachi F-4500 fluorescence spectrophotometer. Solvents used for spectroscopic experiments were
spectrophotometric grade. Absorption and emission spectra were recorded for all compounds in dry degassed
tetrahydrofuran solution at room temperature. Fluorescence quantum yields were measured with respect to 4,4-
difluoro-8-phenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (ΦF = 0.76, λabs = 524 nm, λem = 537
nm, ε = 86,000 M−1cm−1, tetrahydrofuran) [9]. Dyes were excited at 485 nm and excitation and emission slits were
both set to 5 nm [16].
3

2.5. Crystallographic studies
Measurements were made at 150 K on an Oxford Diffraction (Agilent Technologies) Gemini A Ultra diffractometer,
using MoKα radiation (λ = 0.71073 Å) for 6 and CuKα radiation (1.54184 Å) for cis-7. Crystal data and refinement
details are listed in Table 1. Cell parameters were refined from the observed positions of all strong reflections.
Intensities were corrected for absorption using a multifaceted crystal model for 6 [17] and using a semi-empirical
method based on symmetry-equivalent and repeated reflections for cis-7. The structures were solved by direct
methods and refined on F2 values for all unique data. All non-hydrogen atoms were refined anisotropically.
Hydrogens attached to C were positioned with idealized geometry and the thermal parameters constrained using the
riding model with U(H) set at 1.2 times Ueq for the parent atom. The positions of H atoms attached to heteroatoms
(in this case P) were located using peaks in the Fourier difference map and the thermal parameters constrained using
the riding model with U(H) set at 1.5 times Ueq for the parent atom. Oxford Diffraction CrysAlisPro was used for
data collection and processing [18], and Olex2 [19] using SHELXL [20] for structure solution and refinement.
Crystal Impact Diamond was used to generate all other molecular graphics with displacement ellipsoids drawn at the
50% probability level.
Table 1. Crystallographic data and refinement details for 6 and cis-7.
Compound
Chemical formula
Formula weight
[W(CO)5(4)], 6
C30H34B1N2O5P1W1
728.22
Cis-[Mo(CO)4(4)2], Cis-7
C54H68B2MoN4O4P2
1016.62
Temperature
150.0(2) K
150.0(2) K
Radiation, wavelength
Crystal system, space group
Unit cell parameters
MoKα, 0.71073
Monoclinic, P21/c
a = 11.97683(14) Å
CuKα, 1.54178 Å
Triclinic, ⎯P1
a = 10.6543(8) Å α = 87.606(6)°
b = 17.7954(2) Å β = 96.6311(11)° b = 16.1978(12) Å β = 72.343(6)°
c = 28.5950(3) Å
6053.75(13) Å3
8
c = 16.8186(11) Å γ = 73.848°
Cell volume
Z
Calculated density
Absorption coefficient μ
F(000)
Crystal color and size
Data collection method
2653.7(4) Å3
2
1.598 g/cm3
1.272 g/cm3
3.910 mm−1
2.958 mm−1
2896
1068
Orange 0.21 × 0.11 × 0.04 mm3
Xcalibur, Atlas, Gemini ultra
thick-slice ω scans
3.4 to 27.5°
Red, 0.15 × 0.10 × 0.10 mm3
Xcalibur, Atlas, Gemini ultra
thick-slice ω scans
2.8 to 62.8°
θ range for data collection
Index ranges
h −15 to 15, k −21 to 22, l −37 to 37
92956
h −12 to 10, k −18 to 18, l −19 to 18
15468
Reflections collected
Independent reflections
Reflections with F2>2σ
Min. and max. transmission
Data/restraints/parameters
Final R indices [F2>2σ]
R indices (all data)
13134 (Rint = 0.0636)
8145 (Rint = 0.0399)
10062
6872
0.603 and 0.855
13134/8/773
0.736 and 0.744
8145/617/643
R1 = 0.0339, wR2 = 0.0557
R1 = 0.0554, wR2 = 0.0616
1.041
R1 = 0.0651, wR2 = 0.1724
R1 = 0.0755, wR2 = 0.1890
1.034
Goodness-of-fit on F2
Largest diff. peak and hole
0.55 and -0.68 e Å−3
2.14 and −1.10 e Å−3
3. Results and discussion
3.1. Synthesis of the fluorescent primary phosphine 4
The fluorescent primary phosphine 8-((4-phosphino)phenyl)-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-
3a,4a-diaza-s-indacene 4 (Scheme 1) is a derivative of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (abbreviated to F-
Bodipy), which is recognized as being one of the most versatile fluorophores available due to its highly desirable
properties, which include (i) a strong UV absorption profile; (ii) a sharp fluorescence emission peak; (iii) high
quantum yields; (iv) high thermal and photochemical stability; (v) negligible triplet state formation and (vi) good
solubility and chemical robustness [21]. The arylbromide 1 was prepared in a one-pot condensation reaction between
4

3-ethyl-2,4-dimethyl-1-pyrrole and 4-bromobenzaldehyde. A subsequent palladium-catalyzed coupling reaction with
diethylphosphite yielded the fluorescent phosphonate 2. Because the two fluorines do not survive the later reduction
step [22], we treated 2 with two equivalents of methyl magnesium bromide to give 3. This was reduced to 4 using
lithium aluminium hydride and chlorotrimethylsilane as a dual reducing agent (Scheme 1).
Scheme 1. The synthetic procedure for the synthesis of the fluorescent bodipy primary phosphine 4.
As predicted theoretically [23], the experimental 31P-1H NMR spectra showed no oxidation of 4 in d-chloroform
solution or in the solid state over seven days in air. The 31P-1H NMR chemical shift of −121.7 ppm (1JPH = 202.5 Hz)
for 4 is typical for primary phosphines [1, 11]. Phosphine 4 can also be purified by column chromatography on silica
gel in air, which is remarkable for this class of compound, and further demonstrates its air stability. Although the
details of our DFT model are discussed elsewhere [23], it proposes that incorporation of the phosphino group onto
the highly conjugated boron dipyrromethene (Bodipy) skeleton will induce air-stability, as is found experimentally.
Whilst increasing the π-conjugation in a molecule increases the HOMO energy, this correlates with increasing air-
stability in the systems we have investigated. Although this may seem counter-intuitive, recent evidence suggests
that the mechanism of phosphine air oxidation is via reaction of their radical cations with molecular oxygen [23, 24].
From this perspective, we can rationalize that a radical cation generated from a primary phosphine which contains no
or little π-conjugation or heteroatoms (e.g. PMe3, PEt3) will be a highly reactive species, being generated from a
more stable HOMO orbital, and it is plausible that species such as these enter an irreversible oxidative chain reaction
with aerobic oxygen. For the primary phosphines with significant unsaturation/heteroatom presence, their radical
cations are less reactive. In our calculations there appears to be an approximate radical cation SOMO energy
threshold of −10 eV; phosphines (not just primary phosphines) whose SOMO values are above this value have so far
been found to be air-stable. Note that 4 has a calculated SOMO energy of −8.94 eV [12].
3.2. Molybdenum and tungsten carbonyl complexes of the fluorescent primary phosphine 4
In order to ascertain whether the air-stability of 4 affects its ability to coordinate to transition metals, and also to
establish the effect of any complexation on its photophysical properties, 4 was reacted with molybdenum and
tungsten. Molybdenum carbonyl complexes of phosphines are often synthesized in order to gain an insight into the
electronic nature of the phosphine, as the complexes give characteristic IR absorptions in the region dependent upon
the substituents on the phosphorus; better electron donors/poorer acceptors give rise to lower carbonyl stretching
frequencies. Cis-[Mo(CO)4(PR3)2] complexes give A1 carbonyl stretching frequencies that correlate linearly with
those found in the extensively studied [Ni(CO)3(PR3)] series of compounds [25], evading the need to use the highly
toxic [Ni(CO)4] precursor and are thus particularly attractive [26]. [W(CO)5(PR3)] complexes have also been
prepared and their 31P-183W NMR coupling constants have been shown to increase linearly with the stretching
frequencies of the carbonyl E mode [27], and although this correlation was found to be weak for a different series of
complexes prepared by Keiter and Verkade [28], they did establish a linear relationship between higher values of
coupling constant and a greater electronegativity of the substituents on the phosphorus donor, which was discussed
further by McFarlane et al. [29]. In addition, tungsten carbonyl complexes have been used to stabilize alkyl primary
phosphines that have not been observed in the free state [11b, 30] and primary alkynyl and allenylphosphines that are
otherwise highly unstable [11b, 31]. Mathey has shown that [W(CO)5(RPH2)] forms when 7-phosphanorbornadiene
complexes of tungsten pentacarbonyl are reacted with dihydrogen under 20 bar pressure at 150 °C [32], and also that
primary mono-phosphine complexes of both tungsten and molybdenum can be used to prepare metal-bound
Phospha-Wittig reagents that react further to give phosphaalkenes [33]. Furthermore [M(CO)5(RPH2)] complexes of
both tungsten and molybdenum react with 1,2-diethynylbenzene to give complexed benzophosphepins which can be
5

used to generate reactive metal-bound phosphinidenes [34]. For these reasons we thought it would be interesting to
synthesize both the mono-substituted [M(CO)5(4)] and di-substituted [M(CO)4(4)2] family of complexes (M =
molybdenum, tungsten), and to study their structural and spectroscopic properties (Scheme 2). Thus 4 was reacted
with [Mo(CO)6] and [W(CO)6] in THF under UV irradiation, which led to the mono-substituted complexes
[Mo(CO)5(4)] 5 and [W(CO)5(4)] 6, respectively. A d-chloroform solution of 5 gave a downfield peak relative to 4 in
the 31P NMR spectrum at δ −63.5 ppm, with a 1JPH coupling constant of 326.7 Hz, which compares well with the
related [Mo(CO)5(FcCH2PH2)] complex reported by Henderson (Fc = ferrocene; δ −63.2 ppm, 1JPH = 315 Hz) [13b].
The [Mo(CO)5(FcPH2)] derivative recently published by Hey-Hawkins and co-workers [35] gave a comparable 1JPH
coupling constant of 328.0 Hz. The 13C NMR spectrum of 5 showed a doublet splitting of 24.2 Hz on the resonance
at δ 208.8 ppm, which is attributable to the carbonyl trans to the phosphine ligand, by virtue of the larger 2JCP
coupling [35, 36, 37]. The equatorial carbonyls gave a peak at δ 204.7 ppm (2JCP = 9.8 Hz), the lower chemical shift
consistent with those for related complexes (Table 2). The IR spectrum of 5 gave three carbonyl stretching vibrations
at 2076 (A1 cis/eq), 1992 (A1 trans/ax) and 1929 (E) cm-1 in accordance with the C4v point group [36, 37, 38]. The
analogous tungsten complex [W(CO)5(4)] 6 in d-chloroform gave a 31P NMR spectrum which showed a peak at δ
−85.7 ppm with a 1JPH coupling constant of 340.6 Hz, and 183W satellite peaks that are separated by a 1JPW coupling
constant of 222.9 Hz. The related complex [W(CO)5(PhPH2)] gave corresponding values of δ −90.2 ppm, 1JPH of
343.5 Hz and 1JPW of 221 Hz in d6-benzene [29]. The axial carbonyl of 6 gave a peak in the 13C NMR spectrum at δ
198.3 ppm (2JCP = 23.1 Hz) and the equatorial carbons gave a peak at 195.5 ppm (2JCP = 7.2 Hz), both resonances
upfield to that of the molybdenum complex 5, a trend again consistent with the complexes in Table 2 and
[Mo(CO)5(PMe3)] and [W(CO)5(PMe3)]. For the tertiary phosphine complexes this pattern has been discussed in
terms of the π-donor strength of the metal within its triad [36]. The IR values are consistent with the formula given
for 6, with carbonyl bands recorded at 2077, 1973 and 1902 cm-1; the lower wavenumbers relative to the
molybdenum analogue 5 are again consistent with similar comparisons of the group 6 metal primary phosphine
complexes (Table 2) and for the tertiary phosphine complexes [Mo(CO)5(PMe3)] and [W(CO)5(PMe3)] [36]. This is
in accord with the findings of Gilroy et al., who noted that for their series of ferrocenyl-based [M(CO)5(RPH2)]
complexes the extent of π-backbonding based on the values of the A1 carbonyl stretching frequencies increases from
molybdenum to tungsten, following trends in metal electronegativity [38]. A crystalline sample of 6 was analyzed by
X-ray crystallography and the solid state structure determined (Figure 1). The bond lengths and angles (Figure 1)
were found to be comparable with those in the related [W(CO)5(FcCH2CH2PH2)] [38].
Scheme 2. Synthesis of the group 6 complexes [M(CO)5(4)] and cis-[M(CO)4(4)2] (M = Mo, W).
6

Table 2. Selected NMR and IR spectroscopic data for [M(CO)5(RPH2)].
v(CO) A1 v(CO) A1 v(CO)
31P δ 1JP-H
ppm Hz
1JP-W
Hz
-
δ (2JP-C
CO Trans CO Cis
208.8
(24.2)
198.3
(23.1)
)
δ (2JP-C
)
Eq cm-1
Ax cm-1
E cm-1
[Mo(CO)5(4)] 5a
[W(CO)5(4)] 6a
2076
1992
1929
−63.5 326.7
204.7
(9.8)
195.5
(7.2)
2077
1973
1902
−85.7 340.6
222.9
[W(CO)5(PhPH2)]b
[Mo(CO)5FcCH2PH2]c
[Mo(CO)5FcPH2]d
90.2
63.2
81.5
343.5
315
220
2077
2074
1989
1950
1955
1933
-
-
*
*
328.0
208.8
(23.7)
198.1
(22.2)
196.2
(7)
205.0
(9.2)
195.9
(7.1)
192.5
(-)
[W(CO)5FcPH2]d
2073
1935
1968
1987
1980
1916
1926
1952
1945
101.8 341.5
103.1 347
221
216
-
[W(CO)5(PH2CONH2)]e 2077
[Mo(CO)5(1-AdPH2)]f
[W(CO)5(1-AdPH2)]f
2074
2075
28.51 308.16
208.34
(21.99)
205.44
(8.87)
196.93
(6.87)
47.59 321.00 212.53 196.93
(21.82)
a IR recorded neat, NMR in d-chloroform. b NMR in d6-benzene [29]. c IR in petroleum spirit, NMR in d-chloroform [13b]. d IR in
nujol, NMR in d-chloroform [35]. e IR in THF, NMR in d8-THF [39]. f IR in hexane, NMR in d-chloroform [37].
Figure 1. View of the molecular structure of [W(CO)5(4)] 6 with 50% probability displacement ellipsoids (left). Hydrogens bound
to carbon have been omitted for clarity. Selected bond distances [Å] and angles [°]: W1-P1 2.4957(10), P1-C22 1.819(4), W1-C27
2.010(4), C27-01 1.132(4), W1-C31 2.041(5), C31-05 1.141(5); W1-P1-C22 125.21(12), P1-W1-C27 175.89(12). View of the
molecular structure of cis-[Mo(CO)4(4)2] 7 with 50% probability displacement ellipsoids (right). Hydrogen atoms bound to carbon
have been omitted for clarity. Selected bond distances [Å] and angles [°]: Mo–P1 2.4714(13), Mo–P2 2.4829(13), Mo–C53
2.005(5), Mo–C56 2.041(6), C53-01 1.140(6), C56-04 1.137(7), P1–C22 1.827(4); P1–Mo–P2 93.29(4), Mo-P1-C22 120.12(15),
P1–Mo–C53 177.11 (15).
7

During our studies into air-stable chiral primary phosphines [8], we successfully prepared cis-[Mo(CO)4(RPH2)2] by
following Henderson and Alley’s method of reacting two equivalents of FcCH2CH2PH2 with [Mo(CO)4(pip)2] (Fc =
ferrocene, pip = piperidine) [13c]. Therefore, 4 was reacted with cis-[Mo(CO)4(pip)2] in refluxing dichloromethane
to form the di-substituted product cis-[Mo(CO)4(4)2], cis-7 (Scheme 2). Coordination of the phosphine to the
molybdenum resulted in a downfield shift of the 31P{1H} NMR signal from δ −121.7 ppm for the free phosphine to δ
−56.1 ppm for the complex, as expected, and an increased 1JPH coupling was observed from 202.5 Hz for 4 to 318.9
Hz for complex 7. The carbonyl region of the 13C NMR spectrum gave a pseudo-triplet at 207.8 ppm with a splitting
of 2JCP of 9.4 Hz which is assigned to the carbonyls cis to the primary phosphines. The furthest downfield peak at
213.1 ppm appears as a broad doublet of doublets and is attributable to the two carbonyls trans to the phosphine
ligands. This is consistent with the assignment of the carbonyls in cis-[Mo(CO)4(FcPH2)2] [35] and cis-
[Mo(CO)4(PhPH2)2] [40]. Similarly, the IR spectrum further supports the structure of 7 as the cis-isomer, showing
four distinct bands for the two A1, B1, and B2 stretching frequencies at 2029, 1947, 1919 and 1896 cm−1, again
comparing well with the aforementioned analogues. The lowered wavenumbers of the A1 carbonyl stretching
frequencies in cis-7 is consistent with greater backbonding to those ligands compared to 5, as a result of the
introduction of the second phosphine donor. Crystals of cis-7 were grown by slow diffusion (chloroform/pentane)
and its solid state structure is given in Figure 1. Typical phosphorus-molybdenum, phosphorus-carbon and
molybdenum-carbon bond lengths and the phosphorus-molybdenum-carbon bond angles are as expected (Figure 1)
and compare well with those determined for the related complexes cis-[Mo(CO)4(PhPH2)2] [40], cis-
[Mo(CO)4(FcCH2PH2)2] [13b], cis-[Mo(CO)4{1,2-Fc(CH2PH2)2}] [13c], cis-[Mo(CO)4{nBuN(CH2CH2PH2)2}] [41]
and cis-[Mo(CO)4(PH2CONH2)2] [39]. The carbonyls trans to the phosphine ligands exhibit shorter metal-carbon
bond lengths than those trans to another carbonyl, which indicates that the carbonyl ligand has a stronger trans
influence than the primary phosphine 4 (the same is also true for the tungsten complex 6). As a minor product trans-
[Mo(CO)4(4)2] 7 was also observed and isolated by column chromatography in a 11% yield. The complex gave a
triplet of complex multiplets in the 31P-1H NMR spectrum at δ −48.8 ppm (1JPH = 316.5 Hz). Finally cis-
[Mo(CO)4(pip)(4)] 8 was also isolated in very small quantities - the 31P-1H NMR spectrum gave a triplet of triplets at
δ −63.5 ppm (1JPH = 327.7 Hz). In contrast, Henderson et al. showed that the reaction of 1,2-Fc(CH2PH2)2 and cis-
[Mo(CO)4(pip)2] in refluxing dichloromethane produced cis-[Mo(CO)4{1,2-Fc(CH2PH2)2}] as the sole product [13c].
Darensbourg et al. investigated the mechanism of tertiary phosphine coordination to cis-[Mo(CO)4(pip)2] and
showed cis-[Mo(CO)4(pip)(PR3)] species are intermediates in the formation of cis-[Mo(CO)4(PR3)2] [13a].
The corresponding reaction of two equivalents of 4 with cis-[W(CO)4(pip)2] in toluene at 75 °C for 20 h led to
cis-[W(CO)4(4)2] cis-9 as the major product (Scheme 2). Coordination of the phosphine again resulted in a shift of
the 31P{1H}NMR signal from δ −121.7 ppm for the free phosphine to δ −76.9 ppm for the complex, which showed an
increased 1JPH coupling from 202.5 Hz for the uncoordinated primary phosphine 4 to 388.9 Hz for cis-9. The
presence of 183W satellites were also visible on the spectrum, which gave a 1JPW coupling of 217.4 Hz. The 13C NMR
spectrum showed a pseudo-triplet at 199.3 ppm with a splitting of 2JCP of 7.3, which is once again assigned to the
carbonyls cis to the primary phosphines. The furthest downfield peak at 203.5 ppm appears as a broad doublet of
doublets and is attributable to the two carbonyls trans to the phosphine ligands. The carbonyl stretching frequencies
in the IR spectrum of cis-9 are lower than those for the molybdenum analogue cis-7, a pattern also observed for the
mono-phosphine complexes 5 and 6 as discussed earlier, and were recorded at 2026, 1940, 1912 and 1888 cm-1. As
was also observed for the molybdenum complexes, the presence of the second phosphine in cis-9 results in lower
corresponding A1 carbonyl stretching frequencies when compared to the mono-substituted 6. For reference, the
phenylphosphine analogue cis-[W(CO)4(PhPH2)2] gave carbonyl stretching frequencies values of 2026, 1907, 1875
and 1864 cm−1 [15]. In our reaction we isolated none of the trans isomer, however the cis-[W(CO)4(pip)(4)] 10 was
obtained in a 9% yield giving a 31P{1H}NMR signal at δ −85.0 ppm (1JPH = 340.8 Hz, 3JPH = 12.0 Hz, 1JPW
223.2 Hz).
=
3.3. Photophysical data of the primary phosphine 4, 5, 6, cis-7 and cis-9
Photophysical data were collected in dry, nitrogen purged tetrahydrofuran (Table 3). The absorption profiles of
primary phosphine 4 and its predominant molybdenum and tungsten metal-carbonyl complexation products are
represented in Figure 2; the low-energy maxima (λabs) for 4 appears at 512 nm and is assigned to the S0-S1 (π-π*)
8

electronic transition associated with the Bodipy core. The high molar absorption coefficient (ε, 79,000 M−1cm−1) is in
keeping with previous findings for Bodipy compounds [21]. The broader and less intense band seen at ca 375 nm
corresponds to the S0-S2 (π-π*) transition of the boradiazaindacene unit. The fluorescence quantum yield (ΦF) of 0.33
for 4 compares well to the parent bodipy where the phosphino group is replaced by hydrogen, which has a ΦF value
of 0.35 [9]. This observation was not entirely unexpected given the results from our DFT calculations which showed
that phosphorus orbital participation was significant at HOMO−3 for 4 but not at any occupied orbital above [9, 12].
These findings contradict many of the amine examples and the few examples of phosphines conjugated to organic
fluorophores [42] in which the fluorescence is quenched, a phenomenon often attributed to reductive-photoinduced
electron transfer (PeT). Fluorescence quenching of organic dyes in the presence of heavy metals is documented due
to the normally facile accessibility of the triplet state [43].
Table 3. Photophysical data for 4, 5, 6, cis-7 and cis-9.
a
−1
−1
λ
abs (nm) ε (M cm )
em (nm) ΦF
λ
4
512
512
512
79,000
94,000
101,000
148,000
133,000
526
527
527
528
527
0.33
0.25
0.20
0.31
0.31
5 (Mo)
6 (W)
Cis-7 (Mo) 512
Cis-9 (W) 512
Samples were measured in dry, degassed tetrahydrofuran at room temperature. a Fluorescence quantum yields were measured with
respect to 4,4-difluoro-8-phenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene [16]. Dyes were excited at 485 nm.
Figure 2. Absorption and emission spectra of primary phosphine 4 and its metal complexes 5, 6, cis-7 and cis-9, recorded in
tetrahydrofuran at room temperature.
The complexes cis-[Mo(CO)4(4)2] 7 and cis-[W(CO)4(4)2] 9 also showed typical Bodipy absorption curves [21] with
the same absorption maxima as 4 at 512 nm (Table 3). The di-substituted metal complexes have much larger molar
absorption coefficients in comparison to 5 and 6 due to the presence of two Bodipy ligands, which gives values of ε
of 148,000 and 133,000 M−1cm−1 for cis-7 and cis-9, respectively. Room-temperature fluorescence is still detected for
the complexes and the quantum yields are very similar to that of the uncoordinated primary phosphine (compare ΦF
= 0.33 for 4 vs. 0.31 for both cis-7 and cis-9), and thus little quenching is observed despite the presence of the heavy
9

metal in this system (Figure 2). Having described in the introduction how primary phosphine complexes of the group
six metals are ideal precursors to benzophosphepines, phosphinidenes and phosphaalkenes, our findings highlight the
potential to use the complexes described herein in order to prepare highly fluorescent analogues of these exotic
organophosphorus compounds.
4. Conclusion
We have demonstrated that the air-stability of the fluorescent 4 does not hinder its reactivity in transition metal
coordination chemistry, as it readily forms the mono- and di-substituted group 6 metal carbonyl complexes
[Mo(CO)5(4)] 5, [W(CO)5(4)] 6, cis-[Mo(CO)4(4)2] cis-7 and cis-[W(CO)4(4)2] cis-9, whose spectroscopic and
crystallographic properties are consistent with those found for complexes of other primary phosphines. The
complexes retain similar photophysical characteristics to the uncomplexed 4 with, somewhat surprisingly, little
to moderate quenching observed upon coordination. As discussed earlier, [W(CO)5(RPH2)] and
[Mo(CO)5(RPH2)] have been used to prepare benzophosphepines, phosphinidenes and phosphaalkenes, and
therefore 5 and 6 ought to provide a convenient gateway to fluorescent derivatives of each of these ligand
classes. The preparation and characterisation of 5 and 6, together with the di-substituted complexes cis-7 and
cis-9, has also allowed us to gain insight into the electronic nature of 4 and compare it to non-fluorescent
primary phosphine analogues.
Acknowledgements
We thank the EPSRC for a Career Acceleration Fellowship (L.J.H.) and its National Mass Spectrometry Service
Centre, Swansea, UK and a Studentship (J.F.W. also co-funded by High Force Research Ltd.). Also Newcastle
University for a Studentship (L.H.D.).
Supplementary material
1H and 13C NMR spectra of 4, 5, 6, cis- and trans-7, cis-8, cis-9 and cis-10 are provided in the Supplementary
Information together with detailed X-ray crystallographic data for 6 and cis-7.
References
10

[1] (a) L.J. Higham, The Primary Phosphine Renaissance, in: M. Peruzzini, L. Gonsalvi (
Eds.), Phosphorus
Compounds: Advanced Tools in Catalysis and Material Sciences, Springer, Germany, 1-19, (2011) and references
therein; (b) K.V. Katti, N. Pillarsetty, K. Raghuraman, New Vistas in Chemistry and Applications of Primary
Phosphines, in: J.-P. Majoral (Eds.), New Aspects in Phosphorus Chemistry III: Topics in Current Chemistry,
Springer, Germany, 63-118, (2003) and references therein.
[2] (a) K.V. Katti, H. Gali, C.J. Smith, D.E. Berning, Acc. Chem. Res., 32, 9 (1999); (b) H. Gali, T.J. Hoffman, G.L.
Sieckman, N.K. Owen, K.V. Katti, W.A. Volkert, Bioconjugate Chem., 12, 354 (2001).
[3] (a) H. Dorn, R.A. Singh, J.A. Massey, A.J. Lough, I. Manners, Angew. Chem. Int. Ed., 38, 3321 (1999); (b) C.
Limburg, S. Gomez-Ruiz, E. Hey-Hawkins, Dalton Trans., 39, 7217 (2010).
[4] T. Hanaya, H. Yamamoto, Bull. Chem. Soc. Jpn., 62, 2320 (1989).
[5] E.P. Kyba, S.T. Liu, Inorg. Chem., 24, 1613 (1985).
[6] (a) A. Ficks, I. Martinez-Botella, B. Stewart, R.W. Harrington, W. Clegg, L.J. Higham, Chem. Commun., 47,
8274 (2011); (b) A. Ficks, R.M. Hiney, R.W. Harrington, D.G. Gilheany, L.J. Higham, Dalton Trans., 41, 3515
(2012); (c) A. Ficks, R.W. Harrington, L.J. Higham, Dalton Trans., 42, 6302 (2013); (d) J.T. Fleming, A. Ficks, P.G.
Waddell, R.W. Harrington, L.J. Higham, Dalton Trans., 45, 1886, (2016).
[7] (a) B. Stewart, A. Harriman, L.J. Higham, Organometallics, 30, 5338 (2011); (b) B. Stewart, A. Harriman, L.J.
Higham, Air-stable Chiral Primary Phosphines, Part (ii) Predicting the Air-Stability of Phosphines, in: I.J.S.
Fairlamb, J.M. Lynam (Eds.), Specialist Periodical Reports: Organometallic Chemistry, Royal Society of Chemistry,
Cambridge, 2012, pp. 36-47.
[8] (a) R.M. Hiney, L.J. Higham, H. Müller-Bunz, D.G. Gilheany, Angew. Chem. Int. Ed. 45, 7248 (2006); (b) R.M.
Hiney, A. Ficks, H. Muller-Bunz, D.G. Gilheany, L.J. Higham, Air-Stable Chiral Primary Phosphines, Part (i)
Synthesis, Stability and Applications, in: I.J.S. Fairlamb, J.M. Lynam (Eds.), Specialist Periodical Reports:
Organometallic Chemistry, Royal Society of Chemistry, Cambridge, (2011), pp. 27-45.
[9] L.H. Davies, B. Stewart, R.W. Harrington, W. Clegg, L.J. Higham, Angew. Chem. Int. Ed., 51, 4921 (2012).
[10] L.H. Davies, B.B. Kasten, P.D. Benny, R.L. Arrowsmith, H. Ge, S.I. Pascu, S.W. Botchway, W. Clegg, R.W.
Harrington, L.J. Higham, Chem. Commun., 50, 15503 (2014).
[11] (a) J.T. Fleming, L.J. Higham, Coord. Chem. Rev., 297-298, 127, (2015); (b) M. Brynda, Coord. Chem. Rev.,
249, 2013 (2005).
[12] L.H. Davies, B. Stewart, L.J. Higham, Air-Stable, Fluorescent Primary Phosphines, in: I.J.S. Fairlamb, J.M.
Lynam (Eds.), Specialist Periodical Reports: Organometallic Chemistry, Royal Society of Chemistry, Cambridge, 39,
51, (2014).
[13] (a) D.J. Darensbourg, R.L. Kump, Inorg. Chem., 17, 2680 (1978); (b) N.J. Goodwin, W. Henderson, B.K.
Nicholson, J. Fawcett, D.R. Russell, J. Chem. Soc. Dalton Trans., 1785, (1999); (c) W. Henderson, S.R. Alley, J.
Organomet. Chem., 656, 120 (2002).
[14] L.H. Davies, J.F. Wallis, M.R. Probert, L.J. Higham, Synthesis, 46, 2622 (2014).
[15] T.C. Campbell, A.M. Gibson, R. Hart, S.D. Orchard, S.J.A. Pope, G. Reid, J. Organomet. Chem., 592, 296
(1999).
11

[16] (a) A. Coskun, E.U. Akkaya, J. Am. Chem. Soc., 127, 10464 (2005); (b) Y. Gabe, Y. Urano, K. Kikuchi, H.
Kojima, T. Nagano, J. Am. Chem. Soc., 126, 3357 (2004).
[17] R.C. Clark, J.S. Reid, Acta. Cryst., A51, 887 (1995).
[18] CrysAlisPro version 1.171.35; Agilent Technologies (2010).
[19] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl. Cryst., 42, 339 (2009).
[20] G.M. Sheldrick, Acta Cryst., A71, 3 (2015).
[21] (a) A. Loudet, K. Burgess, Chem. Rev., 107, 4891 (2007); (b) G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem.
Int. Ed., 47, 1184, (2008).
[22] The difluoride analogue of 3 was prepared but reduction of this compound with LiAlH4 resulted in
decomposition of the Bodipy backbone.
[23] B. Stewart, A. Harriman, L.J. Higham, Organometallics, 30, 5338 (2011).
[24] (a) S. Yasui, S. Tojo, T. Majima, Org. Biomol. Chem., 4, 2969 (2006); (b) Z.B. Alfassi, P. Neta, B. Beaver, J.
Phys. Chem. A, 101, 2153 (1997).
[25] C.A. Tolman, J. Am. Chem. Soc., 92, 2953 (1970).
[26] D.R. Anton, R.H. Crabtree, Organometallics, 2, 621 (1983).
[27] (a) S.O. Grim, D.A. Wheatland, W. McFarlane, J. Am. Chem. Soc., 89, 5573 (1967); (a) S.O. Grim, D.A.
Wheatland, Inorg. Chem., 8, 1716 (1969).
[28] R.L. Keiter, J. G. Verkade, Inorg. Chem., 8, 2125 (1969).
[29] H.C.E. McFarlane, W. McFarlane, D.S. Rycroft, J. Chem. Soc. Dalton Trans., 1616 (1976).
[30] F. Mercier, F. Mathey, J. Organomet. Chem., 348, 361 (1988).
[31] J.-C. Guillemin, P. Savignac, J.-M. Denis, Inorg. Chem., 30, 2170 (1991).
[32] M.P. Duffy, L.Y. Ting, L. Nicholls, Y. Li, R. Ganguly, F. Mathey, Organometallics, 31, 2936 (2012).
[33] A. Marinetti, S. Bauer, L. Ricard, F. Mathey, Organometallics, 9, 793 (1990).
[34] (a) M.L.G. Borst, R.E. Bulo, D.J. Gibney, Y. Alem, F.J.J. de Kanter, A.W. Ehlers, M. Schakel, M. Lutz, A.L.
Spek, K. Lammertsma, J. Am. Chem. Soc., 127, 16985 (2005); (b) M.L.G. Borst, R.E. Bulo, C.W. Winkel, D.J.
Gibney, A.W. Ehlers, M. Schakel, M. Lutz, A.L. Spek, K. Lammertsma, J. Am. Chem. Soc., 127, 5800 (2005).
[35] J.R.F. Pritzwald-Stegmann, P. Lönnecke, E. Hey-Hawkins, Dalton Trans., 45, 2208 (2016).
[36] M.S. Davies, R.K. Pierens, M.J. Aroney, J. Organomet. Chem., 458, 141 (1993).
[37] J.R. Goerlich, A. Fischer, P.G. Jones, R. Schmutzler, Polyhedron, 12, 2279 (1993).
[38] A.R. Kenaree, E.R. Sauvé, P.J. Ragogna, J.B. Gilroy, Dalton Trans., 45, 2859 (2016).
[39] M.B. Geeson, A.R.Jupp, J.E. McGrady, J.M. Goicoechea, Chem. Commun., 50, 12281 (2014).
[40] T.C. Campbell, A.M. Gibson, R. Hart, S.D. Orchard, S.J.A. Pope, G. Reid, J. Organomet. Chem., 592, 296
(1999).
[41] A. Heßler, S. Kucken, O. Stelzer, W.S. Sheldrick, J. Organomet. Chem., 39, 553 (1998).
[42] (a) N. Inoue, Y. Suzuki, K. Yokoyama, I. Karube, Biosci. Biotechnol. Biochem., 73, 1215 (2009); (b) N. Soh, O.
Sakawaki, K. Makihara, Y. Odo, T. Fukaminato, T. Kawai, M. Irie, T. Imato, Biorg. Med. Chem., 13, 1131 (2005);
(c) M. Onoda, S. Uchiyama, A. Endo, H. Tokuyama, T. Santa, K. Imai, Org. Lett., 5, 1459 (2003); (d) K. Akasaka,
T. Suzuki, H. Ohrui, H. Meguro, Anal. Lett., 20, 731 (1987); (e) J. Pan, J.A. Downing, J.L. McHale, M. Xian, Mol.
Biosyst., 5, 918 (2009); (f) J.C. Vaughan, G.T. Dempsey, E. Sun, X. Zhuang, J. Am. Chem. Soc., 135, 1197 (2013).
[43] (a) A. Kaloudi-Chantzea, N. Karakostas, C.P. Raptopoulou, V. Psycharis, E. Saridakis, J. Griebel, R. Hermann,
G. Pistolis, J. Am. Chem. Soc., 132, 16327 (2010); (b) M.-H. Ha-Thi, M. Penhoat, D. Drouin, M. Blanchard-Desce,
V. Michelet, I. Leray, Chem. Eur. J., 14, 5941 (2008); (c) B. Valeur, Molecular Fluorescence: Principles and
Applications, Wiley-VCH, Weinheim, 2002; (d) W. Wu, J. Zhao, J. Sun, L. Huang, X. Yi, J. Mater. Chem. C, 1, 705
(2013).
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