The coordination chemistry of phosphonites

Article abstract of DOI:10.1016/j.ica.2013.07.041

Transition metal complexes of phosphonites are of interest as catalysts because transition metal complexes of the closely related phosphines (PR ₃), phosphinites (PR₂XR), and phosphites (P(XR) ₃) have excellent catalytic properties for a variety of organic transformations. However, there has been surprisingly little research on the coordination chemistry of phosphonites. To help in remedying this deficiency, we have begun a study of the coordination chemistry of phosphonite ligands. In this project, seven new phosphonite ligands of the type RP(OR′O) (R = phenyl, 2-thienyl; ORO = 1,1′-bi-2-naphthoxy, 4-tert-butylphenoxy, and catechoxy) and their cis-Mo(CO)₄ complexes have been synthesized. The complexes have been characterized by ³¹P, ¹³C, and ¹H NMR spectroscopy, and X-ray crystal structures of four of the complexes have also been determined.

Full text of DOI:10.1016/j.ica.2013.07.041

Inorganica Chimica Acta 407 (2013) 223–230
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
The coordination chemistry of phosphonites
⇑
William C. Corbin, Karen M. Mai, Jason L. Freeman, Samantha D. Hastings, Gary M. Gray
Department of Chemistry, The University of Alabama at Birmingham, Birmingham, AL 25294-1240, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 May 2013
Received in revised form 16 July 2013
Accepted 18 July 2013
Available online 31 July 2013
Transition metal complexes of phosphonites are of interest as catalysts because transition metal com-
plexes of the closely related phosphines (PR3), phosphinites (PR2XR), and phosphites (P(XR)3) have excel-
lent catalytic properties for a variety of organic transformations. However, there has been surprisingly
little research on the coordination chemistry of phosphonites. To help in remedying this deficiency, we
have begun a study of the coordination chemistry of phosphonite ligands. In this project, seven new phos-
phonite ligands of the type RP(OR0O) (R = phenyl, 2-thienyl; ORO = 1,10-bi-2-naphthoxy, 4-tert-butyl-
phenoxy, and catechoxy) and their cis-Mo(CO)4 complexes have been synthesized. The complexes have
been characterized by 31P, 13C, and 1H NMR spectroscopy, and X-ray crystal structures of four of the com-
plexes have also been determined.
Keywords:
Phosphonite
Molybdenum
Electron-donor
NMR
Ó 2013 Elsevier B.V. All rights reserved.
Steric effects
X-ray
1. Introduction
were synthesized and purified by recrystallization [13]. The com-
plexes were characterized using multinuclear NMR spectroscopy
Transition metal complexes with phosphorus-donor ligands are
excellent catalysts for a variety of organic reactions [1–3]. The
large majority of the phosphorus-donor ligands used in these cat-
alysts are either phosphites, phosphinites or phosphines. More re-
cently, transition metal complexes of phosphonites, the fourth
class of phosphorus-donor ligands, have begun to be studied as
catalysts and appear to exhibit interesting catalytic properties
[4,5].
To realize the potential of transition metal complexes of phos-
phonites as catalysts, it is necessary to understand the coordina-
tion chemistry of these ligands and the factors that affect their
steric and electron donor/acceptor properties. However, the coor-
dination chemistry of these ligands is relatively unstudied with
only three X-ray crystal structures of transition metal complexes
of the ligands being reported [6–8]. The transition metal com-
plexes in these structures are quite different, which limits any
comparisons. In addition, all of the complexes have only a single li-
gand while many of the most interesting catalytically active com-
plexes have two phosphonite ligands.
and also by X-ray crystallography when suitable crystals could
be obtained.
2. Experimental
Tetrahydrofuran (THF) was first allowed to stand over magne-
sium sulfate before being distilled from CaH2. It was then distilled
from sodium metal/ benzophenone. Triethylamine (Et3N) was first
allowed to stand over KOH and then was distilled from benzophe-
none/sodium. Dichloromethane (CH2Cl2) was first allowed to stand
over CaH2 then distilled. All of the diols and alcohols used in the
experiments were dried before use: 2,20-biphenol was sublimed
and 1,10-binaphthol and 4-t-butylphenol were crystallized from
toluene after the solution had been azeotropically dried. Dichloro-
phenylphosphine (PhPCl2) was obtained from Aldrich Chemical
Company and was distilled before use. Dichloro-2-thienylphos-
phine [9], Mo(CO)4(nbd) (nbd = [2.2.1]-bicyclohepta-2,5-diene)
[10] and 3a [11] were synthesized using literature methods. All
reactions were carried out in a dry N2 atmosphere using Schlenk
techniques.
Nuclear magnetic resonance (NMR) spectra were taken of chlo-
roform-d solutions of the ligands and complexes. The spectra were
referenced either to internal tetramethylsilane (1H and 13C) or to
external 85% phosphoric acid (31P). The 31P{1H} NMR spectra were
run on a Bruker DRX 400 MHz NMR spectrometer while the 1H and
13C{1H} NMR spectra were run on a Bruker DPX 300 MHz NMR
spectrometer, a Bruker DRX 400 MHz NMR spectrometer or on a
Bruker Avance 700 MHz NMR spectrometer. In the cases where
To provide insight into the coordination chemistry of
phosphonite ligands, the seven phosphonite ligands shown in
Fig. 1 were synthesized by the reactions of the appropriate RPCl2
(R = phenyl, 2-thienyl) with one equivalent of a diol or two
equivalents of an alcohol and were characterized by multinuclear
NMR spectroscopy. Their cis-Mo(CO)4(phosphonite)2 complexes
⇑
Corresponding author. Tel.: +1 2059348094; fax: +1 2059342543.
E-mail address: gmgray@uab.edu (G.M. Gray).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.07.041

224
W.C. Corbin et al. / Inorganica Chimica Acta 407 (2013) 223–230
was evaporated under reduced pressure to yield 0.79 g (79%) of
spectroscopically pure 1a as
white solid. 31P{1H} NMR
(162 MHz, chloroform-d): d 186.01 (s).
(10)
(15)
(8)
a
(7)
(5)
O
O
(1)
(1)
P
P
O
(16)
O
(4)
S
(18)
(13)
2.2. (2,2’-C12H8O2)P(C4H3S), 1b
1a (R = C6H5, R' = C12H6)
1b (C4H3S, R' = C12H6)
A
solution of 5.09 ml (36.4 mmol) of Et3N and 3.38 g
(18.2 mmol) of 2,20-biphenol in 50 ml of THF and a solution of
3.36 g (18.2 mmol) of (C4H3S)PCl2 in 50 ml of THF were added
drop wise and simultaneously to 50 ml of THF over a period of
4 h with stirring. The reaction mixture was then filtered to remove
the triethylamine hydrochloride precipitate. The filtrate was
evaporated under reduced pressure to yield 5.23 g (96.3%) of
a white solid. The solid was dissolved in a 1:4 mixture of
dichloromethane/hexane and filtered through alumina, and the
filtrate was evaporated to dryness to yield the spectroscopically
pure ligand. 31P{1H} NMR (162 MHz, chloroform-d): d 175.48 (s).
(12)
(10)
(19)
(7)
(5)
O
O
(1)
(1)
P
P
O
(26)
O
(4)
(4)
S
(24)
(21)
2a (R = C6H5, R' = C20H8)
2b (C4H3S, R' = C20H8)
(5) O
(7)
O
(1)
(1)
P
P
S
(12)
1H NMR (300 MHz, chloroform-d):
d 7.72 (H2, 1H, ddd,
O
O
(10)
|4J(H2H4)| = 1 Hz, |3J(H2H3)| = 4 Hz, |3J(H2P)| = 7 Hz), 7.61 (H4,
1H, dd, |4J(H4H2)| = 1 Hz, |3J(H4H3)| = 5 Hz), 7.49 (H–C12H8, 2H,
m), 7.31 (H–C12H8, 4H, m), 7.19 (H3, 1H, ddd, |4J(H3P)| = 1 Hz,
|3J(H3H2)| = 4 Hz, |3J(H3H4)| = 5 Hz), 7.00 (H–C12H8, 4H, m).
3a (R = C6H5, R' = C6H4)
3b (R = C6H5, R' = C6H4)
(7)
t
Bu
O
(10)
(1)
P
(13)
t
Bu
O
(16)
2.3. (2,20-C20H12O2)P(C6H5), 2a
4 (R = C6H5, R' = (C6H4-4-But)2)
A solution of 5.11 g (17.8 mmol) of 1,10-bi-2-naphthol and
4.97 mL (35.7 mmol) of Et3N in 50 mL of THF was added drop wise
to a solution of 2.42 mL (17.8 mmol) of PhPCl2 in 50 mL of THF over
the course of one hour. The solution was then filtered through dia-
tomaceous earth to remove the triethylammonium chloride pre-
cipitate, and the filtrate was filtered through 1 cm layers of both
basic and neutral alumina in Schlenk funnels. The filtrate was
evaporated to dryness to yield 6.83 g (98.0%) of spectroscopically
pure 2a as a white solid. 31P{1H} NMR (162 MHz, chloroform-d):
d 184.73 (s).
Fig. 1. Monodentate phosphonite ligands, RP(OR0O) described in this work. The
numbering scheme for the NMR spectral assignments of the carbon atoms is given
by the numbers in parentheses.
the spectra were assigned, the assignment was made from a com-
bination of DEPT 135, 1H–1H COSY, 13C–1H HMBC and 13C–1H HSQC
experiments or by comparison with the assignments made for clo-
sely related compounds. For ligands 1a, 1b, 2a, 2b, 3a and 3b and
their complexes, numbering was started at the carbon directly
bonded to the phosphorus, continued around that ring, extended
to one of the aromatic carbons bonded to an oxygen and finally
continued around that aromatic ring ending with the carbon
bonded to the other oxygen. For ligand 4 and its complex, number-
ing was started at the carbon directly bonded to the phosphorus
and then continued around that ring. Equivalent carbons and
hydrogens of the-ButC6H4O group were then given the same num-
bers starting with the carbon bonded to oxygen, next extending
around the phenylene ring and finally ending on the But group.
Compound purities were determined by C and H elemental
analyses in most cases. The only exceptions to this were made
for 5b and 7b. For both of these compounds, a batch of crystals
containing an X-ray quality crystal was obtained from the rela-
tively nonpolar solvent mixture dichloromethane/hexanes, and
the 13C, 1H and 31P NMR resonances were completely assigned
for the same batch of crystals. In this case, the elemental analysis
does not provide any additional information because the only
impurities would be organic compounds, which, if present, would
have resonances in the NMR spectra. In addition, the 13C, 1H and
31P NMR spectral assignments for 5b and 7b are very similar to
those of 5a and 7a, for which elemental analyses were obtained.
2.4. (2,20-C20H12O2)P(C4H3S), 2b
A solution of 0.561 g (1.96 mmol) of 1,10-bi-2-naphthol and
0.550 mL (3.95 mmol) of Et3N in 25 mL of THF was added drop
wise to a solution of 0.371 g (2.00 mmol) of dichloro-2-thienyl-
phosphine in 25 mL of THF over the course of one hour. The solu-
tion was then filtered through diatomaceous earth to remove the
triethylammonium chloride byproduct, and the filtrate was evapo-
rated to dryness to yield 0.780 g (100%) of crude product as a white
solid. 31P{1H} NMR (162 MHz, chloroform-d): d 173.92 (s).
2.5. (1,2-C6H4O2)P(C4H3S), 3b
A solution of 4.21 g (38.0 mmol) of catechol and 10.6 mL
(76.0 mmol) of Et3N in 50 mL of THF was stirred at room temper-
ature as a solution of 7.07 g (38.0 mmol) of (C4H3S)PCl2 in 40 mL
of THF was added drop wise over a period of one hour. Then the
reaction mixture was filtered through diatomaceous earth to re-
move the triethylammonium chloride byproduct, and the filtrate
was evaporated to dryness to yield a colorless oil. A 31P{1H} NMR
spectrum of this oil indicated that numerous impurities were pres-
ent in addition to the desired product. The oil was distilled under a
vacuum of 200 mtorr. The first fraction, which distilled at 112 °C,
contained product with a small amount of oxidation/hydrolysis
byproduct and weighed 0.880 g (10.4%). 31P{1H} NMR (162 MHz,
chloroform-d): d 164.60 (s).
2.1. (2,20-C12H8O2)P(C6H5), 1a
A solution of 0.635 g (3.42 mmol) of 2,20-biphenol and 0.864 ml
(6.84 mmol) of Et3N in 25 ml of THF was stirred as 0.61 g
(3.4 mmol) of PhPCl2 was added drop wise into the reaction mix-
ture. This mixture was stirred for three hours and was then filtered
to remove the triethylamine hydrochloride precipitate. The filtrate

W.C. Corbin et al. / Inorganica Chimica Acta 407 (2013) 223–230
225
2.6. (4-But-C6H4O)2P(C6H5), 4
C24, s), 121.98 (C24 or C8, s). 1H NMR (400 MHz, chloroform-d):
d
7.78 (C20H12, , 2H, d,
2H, d, |3J(HH)| = 8 Hz), 7.57 (C20H12
A solution of 1.48 g (9.84 mmol) of 4-tert-butylphenol and
1.37 mL (9.84 mmol) of Et3N was stirred at ambient temperature
as 667 lL (4.93 mmol) of PhPCl2 was slowly added to the flask
from a syringe. The reaction mixture was allowed to stir for
30 min and then was filtered to remove the triethylammonium
byproduct. The residue was evaporated to dryness to give a quan-
titative yield of the crude product as a colorless oil. 31P{1H} NMR
(162 MHz, chloroform-d): 160.13 (s).
|3J(HH)| = 9 Hz), 7.52 (H2 & H6, 2H, m), 7.45 (C20H12, 2H, m), 7.38
(C20H12, 2H, m), 7.28 (H3, H4 & H5, 3H, m), 7.22 (C20H12, 1H, m),
7.11 (C20H12, 2H, dd, |3J(HH)| = |3J(HH0)| = 7 Hz), 6.74 (C20H12, 1H,
d, |3J(HH)| = 9 Hz)|. Anal. Calc. for C56H34MoO8P2: C, 67.75; H,
3.45. Found: C, 67.58; H, 3.41%.
2.10. cis-Mo(CO)4{(2,20-C20H12O2)P(C4H3S)}2, 6b
A solution of 0.415 g (1.38 mmol) of Mo(CO)4(nbd) and 1.00 g
(2.51 mmol) of 2b in 125 mL of dichloromethane was stirred at
ambient temperature for one hour. The solution was then evapo-
rated to dryness to give a quantitative yield of the crude product
as a brown solid. This crude product was dissolved in 1:1 dichloro-
methane/hexanes, and the solution was filtered through silica gel.
Multiple recrystallizations from dichloromethane/hexanes yielded
analytically pure product as colorless crystals. 31P{1H} NMR
(162 MHz, chloroform-d): d 204.36 (s). 13C{1H} NMR (175 MHz,
chloroform-d): d 211.48 (trans CO, aq, |2J(PC) + 2J(P0C)| = 26 Hz),
206.79 (cis CO, t, |2J(PC)| = 11 Hz), 149.08 (C5, bs), 148.00 (C24,
s), 139.83 (C1, aq, |1J(PC) + 3J(P0C)| = 22 Hz), 135.72 (C2,
|2J(PC) + 4J(P0C)| = 19 Hz), 132.94 (C13, s), 132.50 (C16, s), 132.48
(C4, s), 131.68 (C21, s), 131.17 (C8, s), 130.31 (C23, s), 129.73
(C7, s), 128.48 (C9 or C20, s), 128.34 (C20 or C9, s), 127.62 (C3,
bs), 127.02 (C14 or C17, s), 126.96 (C17 or C14, s), 126.20 (C11 or
C18, s), 126.13 (C18 or C11, s), 125.15 (C10 or C19, s), 125.12
(C19 or C10, s), 123.94 (C15, s), 123.35 (C14, s), 122.49 (C22, s),
122.18 (C6, s). 1H NMR (700 MHz, chloroform-d): d 7.81 (H9 &
H20, 2H, bd, |3J(HH)| = 8 Hz), 7.69 (H22, 1H, d, |3J(HH)| = 9 Hz),
7.65 (H23, 1H, d, |3J(HH)| = 9 Hz), 7.59 (H7, 1H, d, |3J(HH)| = 9 Hz),
7.40 (H2, H10 & H19, 3H, m), 7.36 (H4, 1H, d, |3J(HH)| = 5 Hz),
7.32 (H12 & H17, 2H, bd, |3J(HH)| = 9 Hz), 7.23 (H11 & H18, 2H,
m), 6.86 (H3, 1H, dd, |3J(HH)| = |3J(HH)| = 4 Hz), 6.66 (H6, 1H, d,
|3J(HH)| = 9 Hz). Anal. Calc. for C52H30MoO8P2S2ꢁ0.25 CH2Cl2: C,
61.16; H, 3.00. Found: C, 61.15; H, 3.10%.
2.7. cis-Mo(CO)4{(2,20-C12H8O2)P(C6H5)}2, 5a
A solution of 0.0436 g (0.145 mmol) of Mo(CO)4(nbd) and
0.0770 g (0.264 mmol) of 1a in 50 ml of degassed dichloromethane
was stirred for 1 h and was then evaporated to dryness under re-
duced pressure to yield 0.072 g (68.9%) of crude product as a brown-
ish solid. This material was dissolved in a dichloromethane/hexanes
mixture, and the solution was filtered through silica gel. The filtrate
was reduced in volume and cooled to ꢀ5 °C to yield colorless
crystals of the analytically pure product. 31P{1H} NMR (162 MHz,
chloroform-d): d 216.02 (s). 13C{1H} (100 MHz, chloroform-d): d
212.36 (cis CO, aq, |2J(PC) + 2J(P0C)| = 25 Hz), 207.51 (trans CO, t,
|2J(PC)| = 11 Hz), 150.29 (C7 & C18, aq, |2J(PC) + 4J(P0C)| = 9 Hz),
139.61 (C1, aq, |1J(PC) + 3J(P0C)| = 31 Hz), 130.31 (C4, s), 129.37
(C12H8, s), 128.55 (C2 & C6, aq, |2J(PC) + 4J(P0C)| = 14 Hz), 128.40
(C12H8, s), 127.19 (C3 & C5, aq, |3J(PC) + 5J(P0C)| = 9 Hz), 124.64
(C12H8, s), 121.83 (C12H8, s). Anal. Calc. for C40.5H27ClMoO8P2: C,
57.62; H, 3.20. Found: C, 57.47; H, 3.22%.
2.8. cis-Mo(CO)4{(2,20-C12H8O2)P(C4H3S)}2, 5b
A solution of 0.189 g (0.630 mmol) of Mo(CO)4(nbd) and 0.376 g
(1.26 mmol) of 1b in 60 ml of degassed dichloromethane was stir-
red for 1 h, and then the reaction mixture was evaporated to dry-
ness under reduced pressure to give a quantitative yield of the
crude product as a brown oily solid. This material was dissolved
in dichloromethane, and the solution was filtered through silica
gel. The spectroscopically pure product was obtained as colorless
crystals by recrystallization from a dichloromethane/hexane mix-
ture. 31P{1H} NMR (162 MHz, chloroform-d): d 204.82 (s). 1H NMR
(400 MHz, chloroform-d): d 7.61 (H2, 1H, m), 7.47 (H4, 1H, d,
|3J(H4H3)| = 5 Hz), 7.45 (C12H8, 2H, m), 7.20 (C12H8, 4H, m), 7.04
(H3, 1H, dd, |3J(H3H4)| = |3J(H3H2)| = 4 Hz), 6.90 (C12H8, 2H, m).
2.11. cis-Mo(CO)4{(1,2-C6H4O2)P(C6H5)}2, 7a
A solution of 0.764 g (2.55 mmol) of Mo(CO)4(nbd) and 1.00 g
(4.62 mmol) of 3a in 50 mL of dichloromethane was stirred at
ambient temperature for one hour. The solution was then evapo-
rated to dryness to give a quantitative yield of the crude product
as a brown solid. This crude product was dissolved in 1:1 dichloro-
methane/hexanes and filtered through silica gel. Multiple recrys-
tallizations from dichloromethane/hexanes yielded analytically
pure product as colorless crystals. 31P{1H} NMR (162 MHz, chloro-
form-d): d 216.88 (s). 13C{1H} NMR (100 MHz, chloroform-d):
210.03 (trans CO, aq, |2J(PC) + 2J(P0C)| = 26 Hz), 205.55 (cis CO, t,
|2J(PC)| = 12 Hz), 147.05 (C7 & C12, aq, |2J(PC) + 4J(P0C)| = 3 Hz),
142.81 (C1, aq, |1J(PC) + 3J(P0C)| = 20. Hz), 131.59 (C4, s), 128.70
(C2 & C6 or C3 & C5, aq, |2J(PC) + 4J(P0C)| or |3J(PC) + 5J(P0C)| = 9 Hz),
2.9. cis-Mo(CO)4{(2,20-C20H12O2)P(C6H5)}2, 6a
A solution of 0.517 g (1.72 mmol) of Mo(CO)4(nbd) and 1.23 g
(3.13 mmol) of 2a in 125 mL of dichloromethane was stirred at
ambient temperature for one hour. The solution was then evapo-
rated to dryness to give a quantitative yield of the crude product
as a brown solid. The crude product was dissolved in 1:1 dichloro-
methane/hexanes, and the solution was filtered through silica gel.
Multiple recrystallizations from dichloromethane/hexanes yielded
the analytically pure product as colorless crystals. 31P{1H} NMR
(162 MHz, chloroform-d): 215.21 (s). 13C{1H} NMR (100 MHz, chlo-
roform-d): d 212.30 (trans CO, aq, |2J(PC) + 2J(P0C)| = 26 Hz), 207.34
(cis CO, t, |2J(PC)| = 12 Hz), 149.83 (C7, aq, |2J(PC) + 4J(P0C)| = 11 Hz),
148.57 (C26, s), 139.28 (C1, aq, |1J(PC) + 3J(P0C)| = 30 Hz), 133.39
(C15 or C18, s), 132.91 (C18 or C15, s), 132.02 (C4, s), 131.46
(C10 & C23, s), 130.84 (C9 or C25, s), 130.09 (C2 & C6, aq,
|2J(PC) + 4J(P0C)| = 15 Hz)), 129.97 (C25 or C9, s), 128.94 (C11 or
128.03 (C3
&
C5 or C2
&
C6, aq, |3J(PC) + 5J(P0C)| or
|2J(PC) + 4J(P0C)| = 15 Hz), 123.33 (C9 & C10, s), 113.10 (C8 & C11,
s). 1H NMR (400 MHz, chloroform-d): 7.56–7.52 (H2 & H6, 2H,
m), 7.34–7.29 (H3, H4 & H5, 3H, m), 6.85–6.92 (H8, H9, H10 &
H11, 4H, m). Anal. Calc. for C28H18MoO8P2: C, 52.52; H, 2.83. Found:
C, 52.73; H, 2.85%.
2.12. cis-Mo(CO)4{(1,2-C6H4O2)P(C4H3S)}2, 7b
A solution 0.654 g (2.18 mmol) of Mo(CO)4(nbd) and 0.880 g
(3.96 mmol) of 3b in 40 mL of dichloromethane was stirred at
room temperature for one hour before the solvent was removed
under vacuum. The crude residue was dissolved in 1:1 dichloro-
methane/hexanes, and the solution was filtered through silica
C22, s), 128.70 (C22 or C11, s), 128.20 (C3
& C5, aq,
|3J(PC) + 5J(P0C)| = 8 Hz), 127.38 (C14, C19, s), 126.58 (C13 or C20,
s), 126.52 (C20 or C13, s), 125.46 (C12 or C21, s), 125.41 (C21 or
C12, s), 124.27 (C16 or C17, s), (C17 or C16, s), 122.97 (C8 or

226
W.C. Corbin et al. / Inorganica Chimica Acta 407 (2013) 223–230
gel. Multiple recrystallizations from dichloromethane/hexanes
yielded 0.225 g (17.4%) of the spectroscopically pure product.
31P{1H} NMR (162 MHz, chloroform-d): d 203.92 (s). 13C{1H} NMR
(175 MHz, chloroform-d): d 209.50 (trans CO, aq, |2J(PC) + 2J(P’C)|
= 27 Hz), 205.01 (cis CO, t, |2J(PC)| = 14 Hz), 146.52 (C5 & C10, s),
143.04 (C1, s), 134.60 (C2, aq, |2J(PC) + 4J(P’C)| = 18 Hz), 132.28
(C4, s), 127.76 (C5, aq, |3J(PC) + 5J(P’C)| = 9 Hz), 126.11 (C9 & C10,
s), 112.78 (C8 & C11, s). 1H NMR (700 MHz, chloroform-d): 7.58
(H2, 1H, bs), 7.52 (H4, 1H, d, |3J(HH)| = 4 Hz), 7.06 (H3, 1H, dd,
|3J(HH)| = 3J(HH)| = 4 Hz), 6.97 (H6, H7, H8 & H9, 4H, s).
systematic absences and intensity statistics. All data collection
was carried out using the CAD4-PC software [12]. The analytical
scattering factors were corrected for both
of anomalous dispersion. All data were corrected for the effects of
absorption and for Lorentz and polarization effects.
D D
f0 and i f00 components
All crystallographic calculations were performed with the Sie-
mens SHELXTL-PC program package [13]. An initial set of non-hydro-
gen atom positions were determined from Direct Methods and the
remainder of the non-hydrogen atoms were located using differ-
ence Fourier maps. All hydrogen atoms were placed in calculated
positions with the appropriate molecular geometry and a d(C–
H) = 0.96 Å. The isotropic thermal parameter associated with each
hydrogen atom was fixed equal to 1.2 times the Ueq of the atom to
which it was bound. Full matrix refinement of the positional and
anisotropic thermal parameters for all non-hydrogen atoms versus
F2 resulted in convergence in all of the structures. The data collec-
tion and structure solution parameters for the four X-ray crystal
structures reported in this paper are summarized in Table 1. ORTEP
diagrams of the four compounds are shown in Figs. 2–5. Crystallo-
graphic data has been deposited with the Cambridge Crystallo-
graphic Database (5a: CCDC 919121, 5b: CCDC 919122, 7b: CCDC
919124, 8: CCDC 919123).
2.13. cis-Mo(CO)4{(4-ButC6H4O)2P(C6H5)}2, 8
A solution of 0.812 g (2.76 mmol) of Mo(CO)4(nbd) and 2.00 g
(4.93 mmol) of 4 in 40 mL of dichloromethane was stirred at room
temperature for 45 min before the solvent was removed under vac-
uum. The crude residue was dissolved in 1:1 dichloromethane/
hexanes, and the solution was filtered through silica gel. Recrystal-
lization from dichloromethane/hexanes yielded 1.14 g (45.8%) of
the analytically pure product. 31P{1H} NMR (chloroform-d): d
179.09 (s). 1H NMR (400 MHz, chloroform-d): d 7.58 (C2 & C6,
2H, m) 7.33 (C3, C4 & C5, 3H, m), 7.18 (C8 & C12 or C9 & C11,
4H, d, |3J(HH)| = 9 Hz), 6.94 (C9 & C11 or C8 & C12, 4H, d,
|3J(HH)| = 9 Hz), 1.24 (H14, 18H). Anal. Calc. for C56H62MoO8P2: C,
65.88; H, 6.12. Found: C, 65.88; H, 6.09%.
3. Results and discussion
3.1. Syntheses and characterizations of the phosphonite ligands and
their cis-Mo(CO)4(phosphonite)2 complexes
2.14. X-ray data collection
The phosphonite ligands were synthesized by reacting triethyl-
amine, PRCl2, and the diols R0(OH)2 in a 2:1:1 mol ratio as shown in
Eq (1). Essentially quantitative yields of the ligands were obtained
For each compound, a suitable single crystal was attached to a
glass fiber with epoxy and aligned upon an Enraf Nonius CAD4 sin-
gle crystal diffractometer under aerobic conditions. Standard peak
search and automatic indexing routines followed by least squares
fits of 25 accurately centered reflections resulted in accurate unit
cell parameters. The space groups were assigned on the basis of
P
Cl
Cl
R'
P
O
+
+
2 Et3N
ð1Þ
R
HO
OH
R
R'
O
Table 1
Crystal data and structure refinement data for 5a, 5b, 7b and 8 (all data sets were collected with Mo Ka radiation (k = 0.71073 Å) at ambient temperature; all refinements were
full-matrix least-squares on F2).
5a
5b
7b
8
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C
40H26MoO8P2
C36H22MoO8P2S2
804.54
C24H14MoO8P2S2
652.35
orthorhombic
Ibca
C56H62MoO8 P2
1020.94
monoclinic
P2(1)/c
792.49
triclinic
P1
triclinic
ꢀ
ꢀ
P1
10.417(2)
12.383(3)
14.842(3)
92.68(3)
106.67(3)
103.23(3)
1772.3(6)
2
10.281(2)
12.357(3)
14.905(3)
95.14(3)
108.29(3)
103.46(3)
1721.4(6)
2
11.150(2)
19.447(4)
24.916(5)
90
90
90
5402.5(19)
8
1.604
0.804
2608
0.3 ꢂ 0.7 ꢂ 0.2
2.09–24.97
0 6 h 6 13, ꢀ1 6 k 6 23,
ꢀ29 6 l 6 1
2632
23.235(5)
11.456(2)
22.373(5)
90
116.09(3)
90
5348.5(19)
4
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.485
0.514
804
1.552
0.647
812
1.268
0.356
2136
)
Crystal size (mm3)
h (°)
0.3 ꢂ 0.7 ꢂ 0.9
2.09–22.48
ꢀ11 6 h 6 11, ꢀ13 6 k 6 1,
ꢀ15 6 l 6 15
5385
0.2 ꢂ 0.6 ꢂ 0.8
0.3 ꢂ 0.4 ꢂ 0.2
2.03–22.48
ꢀ1 6 h 6 24, ꢀ12 6 k 6 1,
ꢀ24 6 l 6 22
8483
2.05–22.48
Index ranges
ꢀ11 6 h 6 10, ꢀ13 6 k 6 13,
ꢀ1 6 l 6 16
Reflections collected
5100
Independent reflections (Rint
Completeness (%)
)
4618 (0.0921)
100.0
4473 (0.0555)
100.0
2372 (0.0205)
100.0
6963 (0.0276)
99.9
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
none
4618/0/461
0.983
empirical
4473/8/461
1.049
none
2372/0/169
1.081
none
6963/0/616
1.040
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0751, wR2 = 0.1835
R1 = 0.1706, wR2 = 0.2241
1.081 and ꢀ1.401
R1 = 0.0555, wR2 = 0.1454
R1 = 0.0902, wR2 = 0.1645
1.061 and ꢀ0.485
R1 = 0.0483, wR2 = 0.1292
R1 = 0.0672, wR2 = 0.1397
0.713 and ꢀ0.617
R1 = 0.0571, wR2 = 0.1509
R1 = 0.1055, wR2 = 0.1732
0.586 and ꢀ1.096
Largest difference in peak and
hole (e Åꢀ3
)

W.C. Corbin et al. / Inorganica Chimica Acta 407 (2013) 223–230
227
with 2,20-biphenol, 1,10-bi-2-naphthol, or 4-tert-butylphenol as
long as the reactants and solvents were dry. All of these ligands
were obtained spectroscopically pure (exhibiting a single resonance
in the 31P{1H} NMR spectrum and with no unexplained resonances
in the 1H NMR and/or 13C NMR spectra). Reactions with catechol to
form the desired ligands 3a and 3b exhibited a previously noted
sided reaction [11]. These ligands were obtained in low yields after
fractional distillations of the reaction mixtures. No attempts were
made to isolate any of the byproducts of these reactions.
The cis-Mo(CO)4(phosphonite)2 complexes were prepared by
the reactions of the phosphonite ligands with Mo(CO)4(norborna-
diene) in moderate to good yields for most of the ligands as shown
in Eq. (2). The catechol-derived ligands, which could not be ob-
tained in good purities, gave the lowest yields of the complexes.
The most likely explanation for the non-quantitative yields of the
complexes of the other ligands is the multiple recrystallizations re-
quired to remove the polymeric byproduct formed by the
norbornadiene.
in 1 ppm). Replacing a bridging R0 group with two nonbridging
4-tBuC6H4 groups causes 20–25 ppm upfield shifts in the 31P{1H}
NMR resonances of both the free (1a, 2a and 3a versus 4) and com-
plexed ligands (5a, 6a and 7a versus 8) suggesting that there is a
ring strain effect in the ligands with bridging R0 groups.
Coordination of the phosphonite ligands to the cis-Mo(CO)4 cen-
ter causes a downfield coordination chemical shift for all of the
31P{1H} NMR resonances. The shift is sensitive to the R0 group
but not to the R group in the ligands. The largest coordination
chemical shifts are observed for the ligands in which R0 is C6H4
(36.60 ppm for 3a and 39.32 ppm for 3b). The coordination chem-
ical shifts for 1a, 1b, 2a and 2b are slightly smaller at 30 1 ppm
while that for 4 is the smallest at 18.96 ppm. The very different
coordination chemical shifts for the ligands with bridging R0 groups
when compared to that of 4, which has two 4-ButC6H4 groups, sug-
gest that the conformational changes upon coordination are quite
different in the two types of phosphonites.
Complexes 6a and 6b were initially obtained as mixtures of dia-
stereomers because racemic 1,10-bi-2-naphthol was used in the
syntheses of phosphonite ligands, 2a and 2b. Multiple fractional
recrystallizations yielded one of the diastereomers as indicated
by the presence of a single resonance in each 31P{1H} NMR spec-
trum. The NMR characterization is reported for this diastereomer
of each complex. Unfortunately, X-ray quality crystals of neither
6a nor 6b could be obtained so the conformations of the ligands
in these complexes are not known.
3.2. X-ray crystal structures of 5a, 5b, 7b and 8
Single crystals of 5a, 5b, 7b and 8 suitable for X-ray crystallog-
raphy were obtained by recrystallization of the complexes from
dichloromethane/hexanes mixtures, and the X-ray crystal struc-
tures of the complexes have been successfully solved and refined.
The structure of 5b contained a disordered 2-thienyl group due
to a 180° rotation about the P–C29 bond. This was modeled by
including both orientations in the structure and constraining the
bonds and angles of the disordered 2-thienyl group to values sim-
ilar to those observed for the other 2-thienyl group. ORTEP dia-
grams for the complexes are shown in Figs. 2–5 and selected
bond lengths and angles are given in Table 3.
All of the complexes exhibit octahedral coordination geometries
at molybdenum with cis-coordinated phosphonite ligands. The cis
coordination of the large phosphonite ligands would be expected
to result in distortions due to an increase in the P–Mo–P bond be-
yond the ideal 90° angle, and this is observed for 5a, 5b and 8.
However, the P–Mo–P angle for 7b is significantly less than 90°
suggesting that the catechol-derived phosphonite ligands can effi-
ciently pack cis to one another. This may be due to the planarity of
the catechol-derived groups as shown in the structure of 7b in
Fig. 4.
O
C
O
C
O
O
R
O
C
C
P
C
Mo
R
R
ð2Þ
+
2
Mo
O
O
P
P
O
C
R'
C
O
O
O
R'
O
O
R'
C
O
The ligands and complexes were characterized by 31P{1H} NMR
spectroscopy. The spectrum of each ligand contained a singlet
31P{1H} NMR resonance as shown in Table 2. This data shows sev-
eral clear relationships between the structures of the phosphonite
ligands and the 31P{1H} NMR chemical shifts of both the free and
complexed ligands. Replacing the phenyl R group (1a, 2a and 3a/
5a, 6a and 7a) with a 2-thienyl R group (1b, 2b and 3b/5b, 6b
and 7b) results in a 10 to 15 ppm upfield shift in the 31P{1H}
NMR resonance of both the free and complexed ligands. This shift
is consistent with the phenyl substituent being more electron
withdrawing than is the 2-thienyl substituent [14]. Changing the
R0 group does not have a strong effect on the chemical shifts of
the 31P{1H} NMR resonances with those of both the free and com-
plexed ligands for R0 = C10H8 (1a versus 1b/5a versus 5b) and for
R0 = C20H12 (2a versus 2b/6a versus 6b) being essentially the same.
The chemical shifts for the free ligands with R0 = C6H4 (3a and 3b)
are 4 to 6 ppm upfield of those with R0 = C10H8 (1a and 1b) or
R0 = C20H12 (2a and 2b) but the chemical shifts of the complexed li-
gands (5a, 6a and 7a/5b, 6b and 7b) are essentially the same (with-
Another aspect of the coordination geometry that is of interest
is that the rotations of the phosphonite ligands about the Mo-P
bonds are insensitive to the nature of the aryl group on the phos-
phorus but vary greatly depending on the diol or monoalcohol that
was used to prepare the phosphonite. Thus, 5a and 5b have similar
rotations about the Mo–P bonds (5a: P2–Mo–P1–C17 = ꢀ102.2(4)°
and
P1–Mo–P2–C35 = ꢀ99.7(4)°
versus
5b:
P2–Mo–P1–
C29 = ꢀ101.4(3)° and P1–Mo–P2–C33 = ꢀ99.0(3)°), but these are
quite different from those in 7b (P0-Mo–P–C3 = ꢀ162.2°) and in 8
(P2–Mo–P1–C25 = 26.6(2)° and P1–Mo–P2–C51 = 26.2(2)°). The
fact that the rotation about the Mo–P bond in 7b is quite different
from those in the other structures is consistent with the closer
packing of the phosphonite ligands in 7b.
A third point of interest in the structures of 5a and 5b is that the
1,3-dioxa-2-phospholane rings in these complexes adopt chiral
conformations in the solid state. The torsion angles about the C–
Table 2
31P{1H} NMR chemical shifts of the phosphonite ligands, L, and their cis-Mo(CO)4L2
complexes.
C
bond between the phenylenes in 5a (C11–C12–C10–
L
d
31P
cis-Mo(CO)4L2
d
31P
C5 = ꢀ45.1(18)°; C23–C28–C30–C29 = ꢀ47.9(16)°) and in 5b
(C16–C11–C10–C5 = ꢀ43.6(11)°; C28–C23–C33–C17 = ꢀ49.0(10)°)
indicate that the chiralities of all four of the 1,3-dioxa-2-phospho-
lane rings are the same. These torsion angles are similar to those
that have been reported for 1,3-dioxa-2-phospholane rings in the
phosphite ligands of cis-Mo(CO)4(phosphite)2 complexes in which
the phosphite ligands are derived from 2,20-biphenol [15,16].
1a
1b
2a
2b
3a
3b
4
186.01
175.48
184.73
173.92
180.28
164.60
160.13
5a
5b
6a
6b
7a
7b
8
216.02
204.82
215.20
204.36
216.88
203.92
179.09

228
W.C. Corbin et al. / Inorganica Chimica Acta 407 (2013) 223–230
Fig. 2. X-ray crystal structure of 5a. The atomic displacement ellipsoids are drawn at the 25% probability level and the hydrogen atoms are omitted for clarity.
Fig. 3. X-ray crystal structure of 5b. The atomic displacement ellipsoids are drawn at the 25% probability level and the hydrogen atoms are omitted for clarity.
A final aspect of interest in the structures of 5a and 5b is the
rotation about the P–Cipso bonds of the phenyl and 2-thienyl
substituents which determines the orientation of the phenyl
and 2-thienyl groups relative the other phosphorus
substituents. The torsion angles about these bonds are similar 5a
(C22–C17–P1–Mo = 144.9(8)°; C40–C35–P2–Mo = 142.8(9)°) and

W.C. Corbin et al. / Inorganica Chimica Acta 407 (2013) 223–230
229
Fig. 4. X-ray crystal structure of 7b. The atomic displacement ellipsoids are drawn at the 25% probability level and the hydrogen atoms are omitted for clarity.
Fig. 5. X-ray crystal structure of 8. The atomic displacement ellipsoids are drawn at the 25% probability level and the hydrogen atoms are omitted for clarity.
in 5b (S10–C29–P1–Mo = 147.9(13)°; S2–C33–P2–Mo = 149.0(3)°)
indicating that the phenyl and 2-thienyl group in each of the li-
gands has a similar orientation.
state conformations of the complexes. Replacing a phenyl group
with a 2-thienyl group causes approximately 10 ppm upfield shifts
in the 31P NMR chemical shifts of the free arylphosphonite ligands
and the cis-Mo(CO)4(arylphosphonite)2 complexes but has no ef-
fect upon the solid state conformation of the complexes. In con-
trast, changing the diol-derived substituent has little effect on
the 31P NMR chemical shifts of the cis-Mo(CO)4(arylphosphonite)2
complexes, but causes significant changes in the solid state confor-
mations of the complex. The relatively independent effects of the
aryl and diol-derived substituents suggest that it should be
possible to use them to independently tune the electron donor
4. Conclusions
The studies of a series of arylphosphonites and their corre-
sponding cis-Mo(CO)4(arylphosphonite)2 complexes reported in
this manuscript demonstrate that aryl and the diol- or monoalco-
hol-derived substituents have quite different effects on the 31P
NMR chemical shifts of the ligands and complexes and on the solid

230
W.C. Corbin et al. / Inorganica Chimica Acta 407 (2013) 223–230
Table 3
Selected bond lengths [Å] and angles [°] for 5a, 5b, 7b and 8. Symmetry equivalents atoms in 7a are labeled with a ‘.
5a
Length
5b
Length
7b
Length
8
Length
C1–O1
C1–Mo
C2–O2
C2–Mo
C3–O3
C3–Mo
C4–O4
C4–Mo
1.127(14)
2.029(13)
1.151(14)
2.013(15)
1.150(13)
2.027(12)
1.138(12)
2.031(12)
2.451(3)
2.435(3)
Angle
C1–O1
C1–Mo
C2–O2
C2–Mo
C3–O3
C3–Mo
C4–O4
C4–Mo
1.132(9)
2.010(8)
1.139(8)
1.997(8)
1.155(8)
2.026(8)
1.117(8)
2.047(8)
2.4454(19)
2.435(2)
Angle
C1–O1
C1–Mo
1.123(7)
2.029(6)
C1–O1
C1–Mo
C2–O2
C2–Mo
C3–O3
C3–Mo
C4–O4
C4–Mo
1.145(8)
2.005(8)
1.129(7)
2.005(7)
1.142(7)
2.033(8)
1.152(7)
2.015(7)
C2–O2
C2–Mo
1.128(7)
2.043(6)
Mo–P1
Mo–P2
5a
Mo–P1
Mo–P2
5b
Mo–P
2.4059(13)
Angle
Mo–P(1)
Mo–P(2)
8
2.4612(17)
2.4688(15)
Angle
7b
C1–Mo–P1
C2–Mo–P1
C3–Mo–P1
C4–Mo–P1
C1–Mo–P2
C2–Mo–P2
C3–Mo–P2
C4–Mo–P2
P2–Mo–P1
O6–P1–Mo
O5–P1–Mo
C17–P1–Mo
O8–P2–Mo
O7–P2–Mo
C35–P2–Mo
172.1(4)
85.8(4)
85.0(4)
93.0(3)
87.7(4)
174.1(3)
91.8(4)
84.9(3)
99.71(10)
121.1(3)
110.2(3)
122.0(4)
121.1(3)
109.3(3)
123.2(4)
C1–Mo–P1
C2–Mo–P1
C4–Mo–P1
C3–Mo–P1
C1–Mo–P2
C2–Mo–P2
C4–Mo–P2
C3–Mo–P2
P2–Mo–P1
O5–P1–Mo
O6–P1–Mo
C29–P1–Mo
O7–P2–Mo
O8–P2–Mo
C33–P2–Mo
173.0(2)
85.9(2)
84.8(2)
93.7(2)
85.8(2)
174.6(2)
92.4(2)
87.3(2)
99.18(6)
121.15(17)
109.44(18)
123.53(19)
122.21(18)
110.26(18)
121.9(2)
C1–Mo–P1
C2–Mo–P1
C3–Mo–P1
C4–Mo–P1
C1–Mo–P2
C2–Mo–P2
C3–Mo–P2
C4–Mo–P2
P1–Mo–P2
O6–P1–Mo
O5–P1–Mo
C25–P1–Mo
O8–P2–Mo
O7–P2–Mo
C51–P2–Mo
176.39(19)
88.39(18)
87.91(18)
95.58(18)
88.08(18)
176.0(2)
95.44(18)
88.5(2)
94.70(5)
121.24(17)
107.35(16)
122.5(2)
122.19(16)
106.87(15)
121.36(19)
C1–Mo–P
C2–Mo–P
92.75(18)
86.83(17)
P–Mo–P0
O4–P–Mo
O3–P–Mo
C3–P–Mo
87.07(6)
119.24(13)
114.68(13)
120.12(18)
abilities and steric properties of these ligands. Given the increasing
importance of these ligands in catalytic applications, this ability to
independently tune these properties should be very useful in the
optimization of the catalysts.
References
[1] L.H. Pignolet (Ed.), Homogeneous Catalysis with Metal Phosphine Complexes,
Plenum, London, 1983 (and references therein).
[2] B. Cornils, W. Herrmann, Applied Homogeneous Catalysis with Organometallic
Compounds vol. 1, 1996 (and references therein).
[3] P.C.J. Kamer, P.W.N.M. van Leeuwen (Ed.), Phosphorus(III) Ligands in
Acknowledgments
Homogeneous Catalysis: Design and Synthesis, John Wiley
Chichester, UK, 2012 (and references therein).
& Sons, Ltd.,
The authors would like to acknowledge NSF for support under
Cooperative Agreements EPS-0814103 and EPS-0903787. J.L.F.
and S.D.H. thank The Alabama EPSCoR Graduate Research Scholars
Program for funding graduate fellowships. The present work also
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Appendix A. Supplementary material
CCDC 919121, 919122, 919124 and 919123 contain the supple-
mentary crystallographic data for 5a, 5b, 7b and 8. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.ica.2013.07.041.