Exhibit 10.1

RECKSON OPERATING PARTNERSHIP, L.P.,

as Issuer

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FIRST SUPPLEMENTAL INDENTURE

Dated as of January 25, 2007

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Supplementing the Indenture, dated as of March 26, 1999, among

Reckson Operating Partnership, L.P., as Issuer, Reckson Associates Realty Corp.,
as Guarantor,
and The Bank of New York, as Trustee.

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THE BANK OF NEW YORK,

as Trustee

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FIRST SUPPLEMENTAL INDENTURE, dated as of January 25, 2007 (this “First
Supplemental Indenture”), to the INDENTURE, dated as of March 26, 1999 (the
“Indenture”), among Reckson Operating Partnership, L.P., a Delaware limited
partnership (the “Issuer”), Reckson Associates Realty Corp., a Maryland
corporation (the “Guarantor” or “Reckson”), and The Bank of New York, a New York
banking corporation, as trustee (the “Trustee”), which governs the terms of the
Issuer’s 4.00% Exchangeable Senior Debentures due 2025 (the “Debentures”),
5.875% Notes due 2014 (the “5.875% Notes”), 5.15% Notes due 2011 (the “5.15%
Notes”), 6.00% Notes due 2007 (the “6.00% Notes due 2007”), 7.75% Notes due 2009
(the “7.75% Notes”) and 6.00% Notes due 2016 (the “6.00% Notes due 2016” and,
together with the Debentures, 5.875% Notes, 5.15% Notes, 6.00% Notes due 2007
and 7.75% Notes, the “Notes”).

WHEREAS, the Debentures are also governed by the terms of the Officers’
Certificate, dated June 27, 2005 (the “Officers’ Certificate”), pursuant to
which the Debentures were established;

WHEREAS, pursuant to the Agreement and Plan of Merger, dated as of August 3,
2006 (the “Merger Agreement”), among the Issuer, the Guarantor, SL Green Realty
Corp., a Maryland corporation (“Purchaser”), Wyoming Acquisition Corp., a
Maryland corporation and wholly-owned subsidiary of Purchaser (“Merger Sub”),
Wyoming Acquisition GP LLC, a Delaware limited liability company (“Acquisition
GP”), and Wyoming Acquisition Partnership LP, a Delaware limited partnership
(“Acquisition LP”), Reckson will be merged (the “Merger”) with and into Merger
Sub and Merger Sub shall be the surviving corporation (the “Surviving
Corporation”), Acquisition LP with merge with and into the Issuer and the Issuer
shall be the surviving partnership (the “Partnership Merger”) and the name of
the Surviving Corporation will be Reckson Associates Realty Corp.;

WHEREAS, the Merger and the Partnership Merger occurred on January 25, 2007;

WHEREAS, Section 901(1) of the Indenture provides that, without the consent of
the Holders, the Issuer, the Guarantor and the Trustee may amend the Indenture
to provide for the assumption of the Guarantor’s obligations to the Holders of
the Notes in the case of a merger or consolidation or a sale of all or
substantially all of such entity’s assets pursuant to Section 803 of the
Indenture;

WHEREAS, the parties hereto wish to amend the Indenture to replace Reckson with
the Surviving Corporation as the Guarantor under the Indenture upon the
consummation of the Merger;

WHEREAS, Section 4.10 of the Officers’ Certificate provides, among other things,
that if the Guarantor is a party to a transaction that constitutes a Public
Acquirer Change of Control, the Issuer may irrevocably elect to change the
exchange obligation of the Guarantor with respect to the Debentures into an
obligation to deliver, upon exchange of Debentures, cash, shares of Acquirer
Common Stock, or a combination thereof, at the election of the Guarantor, in the
same manner as the Guarantor would otherwise be required to satisfy its exchange
obligations in accordance with the provisions of Section 4.12 of the Officers’
Certificate, and, in connection with such election, the Exchange Rate in effect
immediately prior to the effective time of such Public Acquirer Change of
Control will be adjusted in accordance with the provisions of Section 4.10 of
the Officers’ Certificate;

WHEREAS, the parties hereto wish to amend the Indenture to irrevocably elect to
change the exchange obligation of the Guarantor with respect to the Debentures
into an obligation to deliver, upon exchange of Debentures, cash, shares of
common stock of Purchaser, or a combination thereof, at the election of
Purchaser, in the same manner as Purchaser would otherwise be required to
satisfy its exchange obligations in accordance with the provisions of Section
4.12 of the Officers’ Certificate;

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WHEREAS, Section 801 and 803 of the Indenture and Section 4.16 of the Officers’
Certificate provide that following the consummation of any transaction pursuant
to which the Debentures become exchangeable into common stock or other
securities issued by a third party, such third party will fully and
unconditionally guarantee all obligations under the Debentures;

WHEREAS, the parties hereto wish to amend the Indenture to provide for the full
and unconditional guarantee by Purchaser of all obligations under the Debentures
and the Indenture with respect to the Debentures;

WHEREAS, Section 901(9) of the Indenture provides that, without the consent of
the Holders, the Issuer, the Guarantor and the Trustee may amend the Indenture
to cure any ambiguity or to correct or supplement any provision of the Indenture
which may be defective or inconsistent with any other provision in the
Indenture, or to make any other provisions with respect to matters or questions
arising under the Indenture which do not adversely affect the interests of the
Holders of Notes in any material respect;

WHEREAS, the Issuer believes that (i) the Indenture and the Officers’
Certificate should be corrected and supplemented to provide for the adjustment
of the Reference Dividend following the occurrence of a Public Acquirer Change
of Control and (ii) such correction shall not adversely affect the interests of
the Holders of Notes in any material respect;

WHEREAS, the parties wish to amend the Indenture and the Officers’ Certificate
to provide for the adjustment of the Reference Dividend following the occurrence
of a Public Acquirer Change of Control; and

WHEREAS, this First Supplemental Indenture has been duly authorized by all
necessary corporate action on the part of the Issuer.

NOW, THEREFORE, the parties hereto agree as follows for the equal and ratable
benefit of the Holders of the Notes:

ARTICLE I

Amendments

Section 1.01.                             Amendment to Article III of Officers’
Certificate.  As of the effective time of the Merger, the following definition
in Article III of the Officers’ Certificate shall be amended and restated in its
entirety to read as follows:

““Company Common Shares” means shares of common stock, par value $0.01 per
share, of the Company or, following the occurrence of a Public Acquirer Change
of Control and the election by the Operating Partnership to adjust the Exchange
Rate and the exchange right for a Public Acquirer Change of Control as described
in Section 4.10 hereof, shares of Acquirer Common Stock.”

Section 1.02.                             Amendment to Section 4.14(d) of
Officers’ Certificate.  As of the effective time of the Merger and pursuant to
Section 902(9) of the Indenture, Section 4.14(d) of the Officers’ Certificate
shall be amended by the addition of the following paragraphs at the end thereof:

“The Reference Dividend shall also be subject to adjustment following the
Operating Partnership’s election to adjust the exchange right and exchange
obligation in

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connection with a Public Acquirer Change of Control as described in Section
4.10.  Any such adjustment will be effected by adjusting the Reference Dividend
in a manner inversely proportional to the adjustment to the Exchange Rate made
in connection with any such Public Acquirer Change of Control.

Whenever the Reference Dividend is adjusted as herein provided, the Company or
the Operating Partnership shall as promptly as reasonably practicable file with
the Trustee and any Exchange Agent other than the Trustee an Officers’
Certificate setting forth the Reference Dividend after such adjustment and
setting forth a brief statement of the facts requiring such adjustment. 
Promptly after delivery of such certificate, the Company or the Operating
Partnership shall prepare a notice of such adjustment of the Reference Dividend
setting forth the adjusted Reference Dividend and the date on which each
adjustment becomes effective and shall mail such notice of such adjustment of
the Reference Dividend to the holders of the Debentures within 20 Business Days
of the Effective Date of such adjustment.  Failure to deliver such notice shall
not affect the legality or validity of any such adjustment.”

ARTICLE II

Agreement to be Bound; Public Acquirer Change of Control Election

Section 2.01.                             New Guarantor.   As of the effective
time of the Merger and pursuant to Section 803 of the Indenture, the Surviving
Corporation hereby assumes the obligations of Reckson as the Guarantor under the
Guarantee and the performance of every other covenant of the Indenture on the
part of the Guarantor to be performed or observed.  The Surviving Corporation
agrees to become a party to the Indenture and as such will have all of the
rights and be subject to all of the obligations and agreements of the Guarantor
under the Indenture.  The Surviving Corporation agrees to be bound by all of the
provisions of the Indenture relating to the Guarantor and to perform all of the
obligations and agreements relating to the Guarantor under the Indenture.

Section 2.02.                             Purchaser Guarantee of Debentures.  As
of the effective time of the Merger and pursuant to Section 4.16 of the
Officers’ Certificate, Purchaser hereby fully and unconditionally guarantees all
obligations under the Debentures and the Indenture with respect to the
Debentures.

Section 2.03.                             Public Acquirer Change of Control
Election.  As of the effective time of the Merger and pursuant to Section 4.10
of the Officers’ Certificate, the Issuer hereby irrevocably elects to change the
exchange obligation of the Guarantor with respect to the Debentures into an
obligation to deliver, upon exchange of Debentures, cash, shares of common stock
of Purchaser, or a combination thereof, at the election of Purchaser, in the
same manner as Purchaser would otherwise be required to satisfy its exchange
obligations in accordance with the provisions of Section 4.12 of the Officers’
Certificate, and, in connection with such election, the Exchange Rate in effect
immediately prior to the effective time of such Public Acquirer Change of
Control shall be adjusted in accordance with the provisions of Section 4.10 of
the Officers’ Certificate.

ARTICLE III

Miscellaneous

Section 3.01.                             Interpretation.  Upon execution and
delivery of this First Supplemental Indenture and as of the effective time of
the Merger, the Indenture shall be modified and amended in accordance with this
First Supplemental Indenture, and all the terms and conditions of both shall be
read together as

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though they constitute one instrument, except that, in case of conflict, the
provisions of this First Supplemental Indenture shall control. The Indenture, as
modified and amended by this First Supplemental Indenture, is hereby ratified
and confirmed in all respects and shall bind every Holder of Notes.  In case of
conflict between the terms and conditions contained in the Notes and those
contained in the Indenture, as modified and amended by this First Supplemental
Indenture, the provisions of the Indenture, as modified and amended by this
First Supplemental Indenture, shall control.

Section 3.02.                             Conflict with Trust Indenture Act.  If
any provision of this First Supplemental Indenture limits, qualifies or
conflicts with any provision of the TIA that is required under the TIA to be
part of and govern any provision of this First Supplemental Indenture, the
provision of the TIA shall control.  If any provision of this First Supplemental
Indenture modifies or excludes any provision of the TIA that may be so modified
or excluded, the provision of the TIA shall be deemed to apply to the Indenture
as so modified or to be excluded by this First Supplemental Indenture, as the
case may be.

Section 3.03.                             Severability.  In case any provision
in this First Supplemental Indenture shall be invalid, illegal or unenforceable,
the validity, legality and enforceability of the remaining provisions shall not
in any way be affected or impaired thereby.

Section 3.04.                             Defined Terms.  All capitalized terms
not otherwise defined herein shall have the meanings ascribed to them in the
Indenture or, if not defined therein, in the Officers’ Certificate.

Section 3.05.                             Headings.  The Article and
Section headings of this First Supplemental Indenture have been inserted for
convenience of reference only, are not to be considered a part of this First
Supplemental Indenture and shall in no way modify or restrict any of the terms
or provisions hereof.

Section 3.06.                             Benefits of Supplemental Indenture,
etc.  Nothing in this First Supplemental Indenture or the Notes, express or
implied, shall give to any Person, other than the parties hereto and thereto and
their successors hereunder and thereunder and the Holders of the Notes, any
benefit of any legal or equitable right, remedy or claim under the Indenture,
this First Supplemental Indenture or the Notes.

Section 3.07.                             Successors.  All agreements of the
Issuer, the Surviving Corporation and Purchaser in this First Supplemental
Indenture shall bind their successors.  All agreements of the Trustee in this
First Supplemental Indenture shall bind its successors.

Section 3.08.                             Trustee Not Responsible for Recitals. 
The recitals contained herein shall be taken as the statements of the Issuer and
the Trustee assumes no responsibility for their correctness.  The Trustee makes
no representations as to the validity or sufficiency of this First Supplemental
Indenture.

Section 3.09.                             Certain Duties and Responsibilities of
the Trustee.  In entering into this First Supplemental Indenture, the Trustee
shall be entitled to the benefit of every provision of the Indenture relating to
the conduct or affecting the liability or affording protection to the Trustee,
whether or not elsewhere herein so provided.

Section 3.10.                             Governing Law.  THIS FIRST
SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE LAWS OF THE STATE OF NEW YORK.

Section 3.11.                             Counterparts.  The parties may sign
any number of copies of this First Supplemental Indenture.  Each signed copy
shall be an original, but all of them together represent the

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same agreement.  Facsimile transmission of any signature and/or retransmission
of any signature will be deemed the same as delivery of an original.

Section 3.12.                             Effectiveness of Amendments.  The
amendments to the Indenture set forth in this First Supplemental Indenture shall
become effective as of the effective time of the Merger.

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IN WITNESS WHEREOF, each party hereto has caused this First Supplemental
Indenture to be signed by its officer thereunto duly authorized as of the date
first written above.

 

RECKSON OPERATING PARTNERSHIP, L.P., as
Issuer

 

 

 

 

 

By: Reckson Associates Realty Corp., its Managing
General Partner

 

 

 

 

 

By:

/s/ Andrew Levine

 

 

 

Name: Andrew Levine

 

 

Title: Secretary

 

 

 

 

 

 

 

RECKSON ASSOCIATES REALTY CORP., as
Guarantor

 

 

 

 

 

 

 

By:

/s/ Andrew Levine

 

 

 

Name: Andrew Levine

 

 

Title: Secretary

 

 

 

 

 

 

 

THE BANK OF NEW YORK, as Trustee

 

 

 

 

 

 

 

By:

/s/ Julie Salovitch-Miller

 

 

 

Name:Julie Salovitch-Miller

 

 

Title: Vice President

 

 

 

 

 

 

 

SL GREEN REALTY CORP.

 

 

 

 

 

 

 

By:

/s/ Andrew Levine

 

 

 

Name: Andrew Levine

 

 

Title: Executive Vice President

 

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