SCHEDULED MAINTENANCE
Capping calixarenes with metallodiphosphine fragments: towards intracavity reactions
Abstract
The co-ordinative properties of four disubstituted
5,11,17,23-tetra-tert-butyl-25,27-di-RCH
2
O-26,28-
bis(diphenylphosphinomethoxy)calix[4]arenes
[R = C(O)NEt
2
L
1
, C(O)OEt
L
2
, (R)-C(O)NHCH(Me)Ph L
3
or
CH
2
OMe L
4
] have been investigated. Compound
L
1
reacted with
[Au(thf
)(SC
4
H
8
)]BF
4
(thf = tetrahydrofuran,
SC
4
H
8
= tetrahydrothiophene) and
AgBF
4
to yield the chelate complexes
[AuL
1
]BF
4
1 and [AgL
1
]BF
4
2,
respectively. Reaction of L
1
with
trans-[PtH(Cl)(PPh
3
)
2
] resulted in
quantitative formation of trans-[PtH(Cl)L
1
] 3 in
which the platinum hydrogen bond is partially encapsulated within the
calixarene cavity. The structurally related cationic complexes
[PtH(PPh
3
)L
i
]BF
4
(L
i
= L
1
4, L
3
5
or L
4
6), having a PPh
3
ligand trans to
the hydrido ligand, were obtained in high yield by treating
trans-[PtH(thf)(PPh
3
)
2
]BF
4
with diphosphine L
i
. Abstraction of the
chloride ion from 3 with AgBF
4
gave
[PtH(L
1
)]BF
4
7, a complex in which the calixarene
behaves as a tridentate P
2
O
amide
ligand and in
which the metal plane caps one end of the calixarene tunnel. Reaction of
7 with PPh
3
resulted in substitution of the co-ordinated
amide to form 4, while reaction with 4,4′-bipyridine gave the
binuclear complex
[(L
1
)HPt(4,4′-bipy)PtH(L
1
)][BF
4
]
2
8. Reaction of
trans-[PtH(Cl)(PPh
3
)
2
] with
L
i
resulted in a mixture of complexes of general
formula [PtH(PPh
3
)L
i
]Cl (type A)
and [PtH(Cl)L
i
] (type B). The A∶B ratio
depends on the co-ordinating ability of the R groups, since these act as
internal solvent molecules in promoting PPh
3
substitution.
For R groups containing strong donors, e.g. as in L
1
and L
2
, complexes of type B are favoured; with L
4
the reaction leads selectively to [PtH(PPh
3
)L
4
]Cl,
no B-type complex being formed. In at least one case (L
3
) it
was shown that complexes of type A may be converted into the B type.
Reaction of 7 with dimethyl acetylenedicarboxylate gave the insertion
product
trans-P,P′-[Pt(MeO
2
CC![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
CHCO
2
Me)L
1
]BF
4
where the two amides compete
for co-ordination. Complex 7 reacted instantaneously with
tetracyanoethylene (tcne) to yield the platinum(0) complex
[Pt(tcne)L
1
] for which NMR spectra suggest fast flipping of
the co-ordination plane between amides. In contrast to
[Pt(MeO
2
CCCHCO
2
Me)L
1
]BF
4
, strong tridentate P
2
O co-ordination abounds in the
rhodium carbonyl complexes [Rh(CO)L
i
]BF
4
(L
i
= L
1
or L
3
)
obtained from
[Rh(CO)
2
(thf)
2
]BF
4
and the
corresponding diphosphines.
)(SC
4
H
8
)]BF
4
(thf = tetrahydrofuran,
SC
4
H
8
= tetrahydrothiophene) and
AgBF
4
to yield the chelate complexes
[AuL
1
]BF
4
1 and [AgL
1
]BF
4
2,
respectively. Reaction of L
1
with
trans-[PtH(Cl)(PPh
3
)
2
] resulted in
quantitative formation of trans-[PtH(Cl)L
1
] 3 in
which the platinum hydrogen bond is partially encapsulated within the
calixarene cavity. The structurally related cationic complexes
[PtH(PPh
3
)L
i
]BF
4
(L
i
= L
1
4, L
3
5
or L
4
6), having a PPh
3
ligand trans to
the hydrido ligand, were obtained in high yield by treating
trans-[PtH(thf)(PPh
3
)
2
]BF
4
with diphosphine L
i
. Abstraction of the
chloride ion from 3 with AgBF
4
gave
[PtH(L
1
)]BF
4
7, a complex in which the calixarene
behaves as a tridentate P
2
O
amide
ligand and in
which the metal plane caps one end of the calixarene tunnel. Reaction of
7 with PPh
3
resulted in substitution of the co-ordinated
amide to form 4, while reaction with 4,4′-bipyridine gave the
binuclear complex
[(L
1
)HPt(4,4′-bipy)PtH(L
1
)][BF
4
]
2
8. Reaction of
trans-[PtH(Cl)(PPh
3
)
2
] with
L
i
resulted in a mixture of complexes of general
formula [PtH(PPh
3
)L
i
]Cl (type A)
and [PtH(Cl)L
i
] (type B). The A∶B ratio
depends on the co-ordinating ability of the R groups, since these act as
internal solvent molecules in promoting PPh
3
substitution.
For R groups containing strong donors, e.g. as in L
1
and L
2
, complexes of type B are favoured; with L
4
the reaction leads selectively to [PtH(PPh
3
)L
4
]Cl,
no B-type complex being formed. In at least one case (L
3
) it
was shown that complexes of type A may be converted into the B type.
Reaction of 7 with dimethyl acetylenedicarboxylate gave the insertion
product
trans-P,P′-[Pt(MeO
2
CCCHCO
2
Me)L
1
]BF
4
where the two amides compete
for co-ordination. Complex 7 reacted instantaneously with
tetracyanoethylene (tcne) to yield the platinum(0) complex
[Pt(tcne)L
1
] for which NMR spectra suggest fast flipping of
the co-ordination plane between amides. In contrast to
[Pt(MeO
2
CCCHCO
2
Me)L
1
]BF
4
, strong tridentate P
2
O co-ordination abounds in the
rhodium carbonyl complexes [Rh(CO)L
i
]BF
4
(L
i
= L
1
or L
3
)
obtained from
[Rh(CO)
2
(thf)
2
]BF
4
and the
corresponding diphosphines.
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